Today I fixed my dropbox installation on mac os x . It was not updating (sending) files from the Mac to the Dropbox servers. In fact it was sending new files to dropbox servers but some old files that were supposed to be on dropbox account were not synchonized and I couldn’t get Dropbox to notice that, until today. I found this post and it seems that if you close dropbox, delete the ~/.dropbox directory and restart dropbox you’ll get the account linking screen again and dropbox will index everything and make sure that your local Dropbox directory match the online one. It took a while but all the files are safely transferred to Dropbox now.