I recently ran across a very, very difficult problem to diagnose and fix, and I couldn't find this issue going on anywhere else so I thought I'd write about it here in case it comes up again for anyone else. In a Windows Phone 7.1 (i.e. Mango) application...

I had a friend send me kind of an interesting problem the other day. He was trying to add a new user programmatically to a Windows claims site and having all sorts of difficulties. His initial attempt at adding the user with domain\username and the SPRoleAssignment...