There is currently a cap on the number of followers you can track. That is why it says you have too many followers. After you reach that limit, you can no longer check your stats. Tweets will not be posted either if you had that option turned on previously.
You're right, the optout page was indeed producing an error. It was processing requests, so the error was not very obvious from the administrative viewpoint. However, this has been fixed. Also, none of the optout requests were lost despite the error shown.