I've been sharing videos by using the 'copy dropbox link' option with no problem ever. The past 2 times though there's been a line through the play button on the link. When I click it it says 'this file can't be previewed'. This also happens if I right click on file in dropbox and select 'view on dropbox.com'. The file plays fine on my mac and is the same file format as all my previous videos - .mov. It is also less than 3 minutes long. Any ideas what could be the issue?