I'm afraid I have exactly the same problem, Proteus is such a cool app, but it won't work with MSN (keeps disconnecting from the MSN network).
There where some help files to get this sorted on the Proteus home page (in the forum).
I'm going there right know to check it out in fact. I'll be back...
Just updated to the latest version and made sure I scrapped all Proteus keychain files in the Keycahin app, it works!!!