I can't reproduce any issues with Dropbox on any of my tablets, so this is not going to be something I can even investigate. If you need a workaround, install the Dropbox app, log into the account using the app, and then you can use Import->System File Browser in MobileSheets and select the Dropbox app in the left panel. You should then be able to import files through the Dropbox app. I will update the Dropbox library for the next update, so we can see if that helps with the issue at all. Also, just to verify, is this all on Android devices? You posted in the Android subforum, so I'm assuming that is the case, but I just want to check.
Mike
Mike