This happened to me as well. I used the auto-install feature (it’s worked great in the past…) after a full back up and all plug-ins deactivated. Couldn’t access my second side bar, and wasn’t able to drag widgets.
Deactivated all plug-ins, then reactivated them one by one, each time checking to see if I could access my 2nd side bar, etc. It worked! I found the bad plug-in “RSS Icon Widget.” It hadn’t caused problems before the upgrade, though.
