RSOD when an invitee clicks on their invitation link

(Bug, Closed -> Fixed, Priority: Critical, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Invites
Summary: This is after the move to AWS, when I tried to invite people into the Site Book.
Upon looking into it, it looks like a serialization issue: User.Anonymous isn't a case class, so isn't serializable. This never happened before because we were on a single machine, so serialization wasn't happening.