Pidgin says "Unable to add user: Unknown error (204)" on login to MSN

"It took more than a year of not bothering to figure this out, but I finally figured it out.

Do these things:

Log in to MSN on a Windows box. (I know, it hurt me too)
Find that user, and delete them, their account is probably closed anyway
Your Pidgin should work fine again.

I couldn't for the life of me fix this problem with Pidgin alone."