From the message you get i think you're using the "universal"polygamy patch from mess.be. Correct me if im wrong ;\
what version of msn are you running? Though the polygamy patch says its universal(for messenger 5.x) it doesn't work in every case. The instructions from the mess.be download site:
I've used it with 6.2 with no problems, and now all of a sudden when patching it it tells me it didnt work.
=(