Installed Cinnamon but can't log into it

[blacktrance]

I have 12.04 and have just installed Cinnamon. Everything seemed to install fine (no error messages), but when I select to boot into Cinnamon at the login screen, it logs me into Gnome Shell. Cinnamon has installed, because I can see and run "Cinnamon Settings" - but I can't log in. Thanks.

[cblambert]

You must install them one line at a time