If this is really related to upgrading then explore the possibility that the old configuration files were not removed by the upgrade and at the same time the old configuration files are incompatible with the upgraded ubuntuone-client.
Remember that when a new user account is created then those directories and their contents must be created from scratch therefore they will be re-created if you remove them.
If this is really related to upgrading then explore the possibility that the old configuration files were not removed by the upgrade and at the same time the old configuration files are incompatible with the upgraded ubuntuone-client.
Try removing
~/.config/ubuntuone share/ubuntuone
~/.local/
~/.cache/ubuntuone
and rebooting.
Remember that when a new user account is created then those directories and their contents must be created from scratch therefore they will be re-created if you remove them.