I can't validate/complete the registration of my IM - jabber w/ pidgin

I am trying to re-add my IM as a device using a locally managed jabber server. When I enter my ID (username@mydomain.edu) and select jabber as the protocol, it all appears to work on the Twitter end.

However, on my IM client end (Pidgin), it doesn't work. It tells me that I am "Not Authorized" to IM this account (twitter@twitter.com) and I have received no request to add a jabber buddy under this account.

Any suggestions?