Starting a clean compiled monkeymsn, and trying to connect inserting user and password gets me this, and monkeymsn does nothing else.
joel@supernova:~/monkeymessenger$ monkeymsn
(/usr/lib/monkeymsn/monkeymsn.exe:17601): Gtk-CRITICAL **: gtk_box_pack_start: assertion `child->parent == NULL' failed
(/usr/lib/monkeymsn/monkeymsn.exe:17601): GLib-CRITICAL **: g_source_remove: assertion `tag > 0' failed
/contact-list/show-offline
(/usr/lib/monkeymsn/monkeymsn.exe:17601): Gtk-WARNING **: Invite: missing action Invite
System.Net.Sockets.SocketException: The socket is not connected
at System.Net.Sockets.Socket.Shutdown (SocketShutdown how) [0x00000]
at MSNPSharp.Core.SocketMessageProcessor.Disconnect () [0x00000]
at MSNPSharp.NSMessageProcessor.Disconnect () [0x00000]
at MSNPSharp.NSMessageHandler.OnXFRReceived (MSNPSharp.Core.NSMessage message) [0x00000]
at MSNPSharp.NSMessageHandler.HandleMessage (IMessageProcessor sender, MSNPSharp.Core.NetworkMessage message) [0x00000]
Logged In: NO
I second that, with the getdeb package for feisty.
Logged In: YES
user_id=1275342
Originator: NO
This problem can be solved by updating your mono-libraries!