ITunes will NOT deauthorize my iPhone

I am attempting to remove my iPhone from my mother's account as she has reached her five computer limit. I go to Account > Authorizations > Deauthorize This Computer. I sign in, and click on Deauthorize. It will tell me that the computer is not authorize, and to play a song or video purchased on iTunes to authorize it. It will do this while I'm listening to a song purchased on iTunes.