The internal drive which hosts my Dropbox Folder was nearing capacity, so I stopped syncing via the Dropbox menu. I then selected all the folders that I didn't need downloaded to my computer and selected "Make Online Only". After a moment, I was told that the Dropbox Helper application wasn't responding, and to quit and relaunch Dropbox. So I quit the Dropbox application from the menu, but it would no longer re-launch, stating that there was an error of some sort.
I proceeded to restart my computer, but this did not solve the problem. So I attempted to re-install Dropbox in order to ensure that I had the latest version.
After downloading, the Dropbox Installer attempted to run, but ran into a problem, stating that it couldn't download the program; it asked if I wanted to try a different downloader (this despite the fact that it was in the Install phase of the process). So I downloaded the Dropbox Offline Installer (Dropbox 175.4.5569.dmg). After opening it, the Dropbox menu appears for awhile; opening the menu shows the Starting Up animation. After some time however, it errors out, and states as before that it cannot launch. A text dump is provided, the relevant bit I think being this:
"The executable currently located at file:///private/var/folders/wl/[...]/T/AppTranslocation/[...]/d/Dropbox.app/ is translocated and can't be launched., NSLocalizedDescription=The application cannot be used from this location." (Elipses added by me.)
Obviously I have not moved the application file anywhere, I am merely running the installer. It sounds like a permissions issue, but that is not something that is generally user-addressable these days (Apple removed the "Repair Permissions" option from Disk Utility many years ago).