In ubuntu 11.10 I had problems adding my google calendar .
In gconf-editor, I found the evolution entry in apps/evolution
there is a key called “source” in addressbook and calendar also, and they differ. the calendar had no “google” source. I simply copied it from the addressbook part (double click on sources under addressbook, select the one with name=”Google”, press edit, copy it’s content) and added a new entry to the source key under calendar (same procedure, but press add when editing the key).
Got that from ubuntuforums.org