In our case we got event code: 4005 and event message: Forms authentication failed for the request. Reason: The ticket supplied was invalid. The solution was ME2661403
: ASP.NET applications rejecting requests having MaxHttpCollectionKeys greater than 1000.
From a newsgroup post: "For some reason, I always got a failure when logging in. I am sure I was entering the correct password, and I have deleted and re-added the user. I remembered that the database is automatically recreated if it is deleted, so just to make sure everything was OK with the database, I decided to move it somewhere else, so that .Net would automatically re-create it. This worked, and after I re-added the users & roles, everything works now. It seems there was something wrong with the database".