Comment 3 for bug 984340

This is because there is a mismatch between the ubuntuone-syncdaemon staying around from the older version and ubuntuone-control-panel from 3.0.0 after upgrading. Have you restarted your computer?

Unfortunately the upgrade process does not specify to restart nor does it stop the old Ubuntu One processes, but either restarting or stopping all existing ubuntuone processes should allow you to have a functioning Ubuntu One 3.0.0 installation.