Re 1601/1603 problem when MSN messenger “asks” you to upgrade – after trying many fixes with NO sucess, variously trying to reinstal MSN (including 6.2 not yet official), and playing with the registry, I simply killed MSN Messenger (Add/Remove, AND deleting directory was necessary) and installed Windows Messenger.

My advice. Skip the torment, kill MSN Messenger and go to Windows Messenger.