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“Can't open the file because the file format/extension is not valid.” error on website/desktop app.

Hi,

I’m having a serious issue with Dropbox where many of my files appear in the correct folders on both my computer and on Dropbox.com, but none of those specific files will open. I receive errors like:

“Cannot open the file because the file format or file extension is not valid.”

Here’s what’s happening:

I can see the file names and folder structure in Explorer.
I can also see the same file names on Dropbox.com.
But when I try to open any of these files (locally or on the web), they fail with format/extension errors.
The files appear to be zero‑byte placeholders rather than real files.
Most of my other files still exist on my second laptop, but the ones I urgently need do not.
These missing files appear in Dropbox, but none of them open anywhere.

This all started after repeated issues with the Dropbox sync engine failing to start. Dropbox would install, but the app never launched, no tray icon appeared, and the sync engine seemed to be stuck in a crash loop. I believe this may have caused Dropbox to replace some of my original files with empty placeholder versions.

I need help determining:

Whether Dropbox has older historical versions of these files stored internally.
Whether a data recovery review is possible for these zero‑byte or corrupted placeholder files.
Whether Dropbox can confirm if these files ever successfully uploaded before the sync engine failed.

These files are extremely important to me, and I’m hoping Dropbox Support can check server‑side logs or historical versions to see if recovery is possible.

Thank you for any help or escalation you can provide.

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Nancy

Thanks for posting on our Community, @Mitz1.

First off, I’d like to clarify that we’re not the support team (your support options may differ based on your plan) and we can’t see account-specific info here on the forum. There are still a few things to check together though, in order to determine what may have happened.

Now, can you clarify if you can see the Dropbox icon in your system tray/menu bar at the moment? If the Dropbox app seems to be syncing now, I’d like to know its syncing status.

Other than that, I’d like two separate screenshots of the files you can’t open; one screenshot of what you see on your Dropbox account online and one more of what you see on your desktop app (including any sync icons you may be seeing next to those files).

In general, Dropbox allows you to recover previous versions of files for a specific period of time, which depends on your current Dropbox plan. However, I’d like us to gather a few more details first, to isolate the issue.

Let me know once you have more info.

garrycoach

Since they fail to open on the web too, the zero-byte placeholder likely overwrote the actual data during that sync crash.

Go to Dropbox .com, right-click one of the broken files, and hit Version History. You're looking for an older version with an actual file size (not 0 bytes). If the only version listed is the current empty one, the real data probably never left your drive before the crash.

Mitz1

From the Start Menu, I launched the Dropbox App and this is the window that came up. I know it’s small, but the tray window bar on the bottom right show that the Dropbox app is not running as there is no tray icon. The syne engine never starts. I can see the files, but they do not open.

Next is a screen shot is from the Dropbox web. None of these will open from this window. However, on my other laptop I can open all of these EXCEPT the bottom file dated 1/27/2026. That file doesn’t even show up on my other computer. The reason I tried to relink/resync my primary computer was for this reason. Files were missing from the other computer. Something changed around the middle of January and anything that was added after around that date did not show up on computer 2.

It appears to me that during the attempted update, the files were corrupted.

As a side note: Yesterday with the help of a friend, I was finally able to recover at least the file names in my Dropbox folder. I had high hopes that they would open. When I double clicked a file, the first window that came up was that I could not open the file because I was out of memory and it asked me if I wanted to upgrade. I checked my records and confirmed that on June 07, 2025, I had paid $119.88 for an annual Dropbox Plus subscription. Because I was desperate to get that file back, I upgraded to the recommended subscription, which was the same price, $119.88. I received a confirmation email that I had been charged, restarted my computer but none of those files would open and gave me a format or extension not valid error message.

I do not know what kind of support I can expect with the Dropbox Plus subscription. I’m hoping the forum can help me.

Hannah

Thanks for the update and the screenshots, @Mitz1.

From what I can see on your first screenshot, you do have the Dropbox icon in your system tray.

It's not in the list of hidden icons, it's the one right next to your WiFi icon; can you hover over it with your mouse and let us know what you see?

Mitz1

Hannah, I didn't realize that was the Dropbox icon. When I was attempting to reload the DB App over the weekend, everytime it lauched it just gave me a new Dropbox window but without any files. I wish I could go back now and see it that icon was there at the time.

Thanks for your help.

Hannah

Not a problem, @Mitz1!

Did that help you figure out the issue?

If you still need help, let me know what you see when you hover over that icon, so I know the app's sync status and version and assist you further.

Mitz1

Hannah

Thanks for that, @Mitz1. The app should be syncing as normal.

And it's definitely strange that you can't open the files online.

Have you tried restoring one of the files that gives you this error to an older version, to see if it opens then?

Mitz1

Nothing opens on this primary computer. Nothing! On computer 2 I can still open every file create before mid January,

Nancy

Can you send me one more screenshot of what you see on the Dropbox website, when trying to open one of those files?

I’d also like you to right-click on one of your files on the desktop app next and send me a screenshot of the options you see. Do you see an option to make the file available offline, or online-only?

Mitz1

Nancy, Your 1st request: screenshot of DB website when trying to open a file. I picked the file “2024 Futures Trading.xlsx” because this file opens perfectly on Laptop 2

Upon seeing this message, I hit the Download button and something did download but here is a screen shot tell me about file extension.

Your 2nd request: right-click on one of your files on the desktop app. As you can see, there is an option to make the file available offline, or online-only.

As a side note, if it is relevant, in regard to Hannah’s question about the system tray. Even though the Dropbox App was launched from the Start Menu, the icon is not present on the System Tray.

Mitz1

I receive an email that my last post is delayed. I'm going to attempt to post it again shortly.

Megan

Hey @Mitz1, let me jump in here!

You mentioned throughout this thread that some of the files appear to have zero size placeholders. However, it's important to point out that on your screenshots it looks like the content has an actual size.

Can you send me a screenshot, and let me know where exactly these files appear as 0 size? Does this happen when you visit your account online, or locally?

In addition to that, it seems that some of the files have a double extension. Can you try removing the last one, and check if anything changes after that?

One more thing to note is that Excel has a built-in tool used to fix corrupted files called "Open and Repair". I think it'd be useful to give this one a go too, while you're at it.

As a last step, I'd suggest that you move some of these example files outside of your Dropbox folder (you can try moving them to your Desktop) and see if the behavior remains the same.

In any case, I'll be waiting for your updates!

Mitz1

Hello Megan, thank you for jumping in.

Regarding the zero place holders. Yes, the screen shot I took does show files sizes. This is very confusing to me and I’m going to try to recall what happened. At some point over the weekend when I was working to recover files, I’m pretty sure that all the file sizes were zero, Or it may have been that I couldn’t even see any files. On Monday, with the help of a friend I was able to bring back my file list. When I tried opening a file from that list, I got an error message saying I was out of memory. I checked my records and found I had renewed my Dropbox Plus subscription last June. I bought the new subscription anyway hoping that it would allow me to recover my files. That didn’t work.

Regarding file extensions. Yes, they appear to have changed, but only on my primary computer. On my second computer, the HP, they open fine…except for files created sometime around mid-January (which don’t even show up on the HP). I also tried downloading some files and changing the extension but that didn’t work either.

Regarding Excel “Open and Repair”, as I’ve stated, the files open perfectly on my HP computer.

Regarding moving the files. I am in the process of copying the files from my HP.

A sync problem happened sometime in January when the files created on my primary computer were not showing up in Dropbox on my Computer 2, the HP. That is why I tried to resync in the first place.

I use a program everyday called Tradestation to track charts and keep notes. Every time I make a change to a chart, I need to save and it overrides the previous version. Unfortunately, for years now, I have been saving these files on Dropbox, so when I open Tradestation it looks for the file to open up. Those files took me years to accumulate. And now, it appears they are gone.

I appreciate your help. Let me know what other information I can provide.

Don [removed]

[removed]

[personal info removed per the Dropbox Community Guidelines]

Hannah

Thanks for the update, Don, it is a pretty strange situation.

One more thing I'd like you to check is the syncing icon next to the files that are not opening; are the files set to "online-only"?

If so, can you right-click on them, choose "make available offline" and then try to open them to see if that makes a difference?

Mitz1

Hannah, in response to your post. I cannot tell for sure if they are set to “online-only”. I hope you can see from this screen shot that an option to “make available offline” is not available.

Don

Jay

Hi @Mitz1, the green icon next to the files indicates that they are already available offline.

Is this only occurring for the Excel files? Are they only for files in this folder, or does it occur for new files that you create within the Dropbox folder?

Regarding the message about being out of memory, are you referring to the Dropbox site, or the computer itself saying there's not enough storage space?

Mitz1

Jay,

Regarding the green icons. Most of these files are available on my computer 2 the HP Desktop Dropbox App. However, this screen shot is from my primary computer and NONE of these files open from the Dropbox App on this computer.

Using the Dropbox Web, NO files open on either machine.

I’ve tried to explain this before, but any files created or saved on my primary computer after around mid-January, only show up on this primary computer Dropbox App. I can not see them on any Web site or my computer 2 App. This is the reason I attempted to resync over the weekend.

It’s not just some Excel files. I use a program called Tradestation. When I create a workspace in that program, it must be saved. Many of these .tsw files were saved after mid-January and are also corrupt.

When you save an existing workspace, it saves over the previous version.

I only have two or three Excel files that were saved after mid-January and they are shown on primary computers’ desktop App, but they of course don’t open. There are very important files to me.

On Monday when I was first able to recover the file list on my primary computer desktop App, I had high hopes that they had been recovered. When I tried to open a file, I got a message from Dropbox that said that I was out of Dropbox memory and that I could upgrade my Dropbox memory for an additional charge from Dropbox of $119.88 I had already renewed my Dropbox Plus account last June, but I followed the instructions and bought it anyway. BTW, I was not even close to being out of Dropbox memory. My primary computer has over 300 GB storage space available.

No files created or saved after mid-January will open. I don’t have an exact date in January when this first happened.

I hope you can help me recover my corruupt files.

Don

Mitz1

To all concerned. Here is what I believe is happening.

On my primary computer the Falcon, Dropbox is not running at all. The sync engine doesn't seem to launch, so the app cannot verify the file status and the files do not open. The Dropbox folder itself opens and lists all the files including the most recent ones I'm trying to recover.

On every computer I own, the Dropbox web app also fails to open any files.

On my secondary computer 2, (the HP) the Dropbox desktop app does run, and I can open most of my files there. However, the most recent files do not appear on that machine at all.

From my secondary computer 2 (the HP) I have been able to download and save all the files that still exist in Dropbox, except for those most recent ones. Those files appear in the Dropbox folder on the Falcon, but they do not open anywhere (Falcon, HP, or Dropbox.com).

At this point, I’m simply trying to get Dropbox reinstalled and running again on the Falcon. I understand that the most recent files are likely unrecoverable, and I’ve accepted that. I just need help getting the Dropbox app working again on my primary computer.
Thank you. Don

Hannah

Thanks for the updates, Don.

I completely understand where you're coming from, I would be frustrated if this happened to me as well.

Regarding the Dropbox app, have you tried simply reinstalling it, without uninstalling it first?

And as for your files, if you upload them to the website from the second computer, are you able to open them?

Hopefully, the reinstall will also fix the syncing issue on the Falcon too, but let me know how it goes.

Mitz1

Hannah, thanks for the reply.
Just to clarify: the Dropbox website does not open any files on any of my computers, so uploading files to the website wouldn’t help in this case.

Also, I can already open all of my existing files from the second computer (the HP). The only files I cannot open are the most recent ones, which do not appear on the HP at all and also won’t open on the Falcon or on Dropbox.com.

At this point, I’m mainly trying to get Dropbox running again on my primary computer (the Falcon), since the app does not launch. I'm looking for some help to do this properly.

Don

Hannah

Okay, Don, understood.

Have you tried reinstalling the app like I suggested in my previous reply?

If simply reinstalling the app doesn't work, you can uninstall it, restart the computer and then reinstall it.

Mitz1

Hi Hannah, thanks for the follow‑up.

I tried reinstalling the app exactly as you suggested. Then uninstalling and reinstalling. When I launch Dropbox, a window flashes for about a second with a message I can’t read, and then it closes immediately. After that, the Dropbox folder opens, but the Dropbox app itself never launches. There is no tray icon and no sync engine running.

None of the files in the Dropbox folder on the Falcon will open, and the behavior is exactly the same as before the reinstall.

Please advise on the next steps.

Hannah

Hmm, I see.

In that case, please try our advanced reinstall steps here and we'll go from there.

Mitz1

Dear Hannah,

Before I go any further with the Advanced Reinstall steps, I want to clarify a couple of things.

During the uninstall, Dropbox gave me an option to drag the Dropbox folder into the Recycle Bin, which I did, and then I emptied the Recycle Bin. I’m mentioning this because the Advanced Reinstall instructions say not to delete the main Dropbox folder, but the uninstaller itself prompted me to remove it.

Next, in the Registry Editor, I do not see a “Dropbox” folder directly under HKEY_LOCAL_MACHINE. However, under HKEY_LOCAL_MACHINE → SOFTWARE → WOW6432Node, I do see a Dropbox Update folder, and inside that are two folders: ClientState and ClientStateMedium.

Before I proceed, can you confirm exactly which registry folders I should delete?

I’d like to hear back from you before continuing.

— Don

Hannah

Hi again, Don!

So, regarding the Dropbox folder, it should be okay that you deleted it; it's basically just to keep a copy locally just in case, but that's that.

As for the registry, you can delete the Dropbox Update folder from WOW6432Node, that's the correct one.