We've fixed one of the Dropbox issues that some users were facing. If you were an affected user, then the next time you try to upload, you will be asked to reauthenticate your Dropbox account. After doing so, you should be able to upload without any further problems.
This fix doesn't account for all possible issues, however, so if you still encounter Dropbox problems, please be patient as we work on further improvements. As always, you can help us out by sending error logs when prompted.