For what I read on other MSN clients too is:
For you new posters MSN has updated only last night and since then anything non MSN wont work
So no client other than the original Microsoft shitty one works. I hope aMSN can find a workaround, as I've been using aMSN since MSN 7.0 came out which I didn't like.
Yeah I too have the same problem with aMSN (which I love , great prog)
FYI , other Clients can still work fine , I just tried Pidgen portable and it logs in fine to MSN