I am assuming the user has been associated with a record somewhere else and so you have a dependency, some kind of referential integrity check. I *think* I reported this before but could not find any evidence that I had done.
I have made all of those I wish to delete as "inactive" but it is a clutter problem, especially when using BG stats I see all those inactive users in the list, and people who sync to the board get confused on which players to use. I know, 3rd world problem, but hey, wouldn't it be cool to have it fixed. LOL! Thanks guys.