I use UbuntuOne on Ubuntu 12.04 and Windows 7. Everything synchronized fine for several months until a few weeks ago when UbuntuOne on Windows offered an update which I installed. Now my files on Windows 7 no longer sync even though it recognizes my username and password. It tries to sync and then quits. How do I fix this?
Pull all of your files from both systems (just move them into a new folder) out of UbuntuOne's view, restart it, then re add the files. It seems like it's confused on what it has properly synched and what it has not.