Comment 5 for bug 624445

The fix for the authentication failures in Maverick should be available in the next day or two. In the meantime their is a workaround if you would like to try it.

Open a Terminal and run:

gksudo gedit /usr/lib/pymodules/python2.6/ubuntu_sso/main.py

Near the top of the document, change the http to https in the following line :
PING_URL = "http://edge.one.ubuntu.com/oauth/sso-finished-so-get-tokens/"
so it would be:
PING_URL = "https://edge.one.ubuntu.com/oauth/sso-finished-so-get-tokens/"
Save and close the file.

Restart all the Ubuntu processes. You can do that by running this command:
killall ubuntu-sso-login; u1sdtool -q

Then open Ubuntu One (System > Preferences > Ubuntu One)

You will now if it worked if under the 'Devices' Tab it changes to your computers name instead of <Local Machine>.

thank you,
duanedesign