Comment 9 for bug 576263

I'm sorry to hear that did not resolve the issue. Can you try the following and let us know the results?

   1. Quit the Ubuntu One client (open a terminal window & run "u1sdtool -q; killall ubuntuone-login" without the quotes)
   2. Open Applications->Accessories->Passwords and Encryption Keys
   3. Click on the plus symbol next to "Passwords: login" to expand the list
   4. Right-click on the Ubuntu One token and select "Delete"
   5. Go to https://one.ubuntu.com/account/machines/
   6. Click on the checkbox next to your computer
   7. Click the "Remove selected computers" button
   8. Open System --> Preferences -->Ubuntu One
   9. a web page should open, prompting you to add your computer to your Ubuntu One account
  10. Add your computer

Thanks in advance!