ROOT_MISMATCH in syncdaemon.log - This normally indicates that there may be two Ubuntu One accounts, one in the local cache and another setup in the keyring. This happens if the user installed Ubuntu One with one account and then sets up the computer again with a different account (but all the old Ubuntu One files in ~/.local/share/ubuntuone are still there under the old account). Working around this:
Open Applications->Accessories->Terminal and run:
u1sdtool -q; killall ubuntuone-login ubuntuone-preferences;
sudo rm -rf ~/.local/share/ubuntuone
rm -rf ~/.cache/ubuntuone
rm -rf ~/.config/ubuntuone
mv ~/Ubuntu\ One/ ~/Ubuntu\ One_old/
Open Applications->Accessories->Passwords and Encryption Keys, go to the Passwords tab, delete the Ubuntu One and Desktopcouch tokens by right-clicking on them and selecting "Delete".
Back in a terminal session, run:
u1sdtool -q; killall ubuntuone-login; u1sdtool -c
To get things functioning again, all I had to do was delete my ~/.local/share/ubuntuone directory as indicated above. The u1sdtool line noted above did nothing for me. I mention this just so you do not stop prematurely. Hope this helps.