Hey,
Are you using Windows Vista? If so, this erros are known and common, you'll have to wait.
If not:
Is this in WLM (Windows Live Messenger) or
MSN (Messenger) (Your title says MSN so I'm going to go with that...)
If you updated to Msg Plus! Live, then that is the reason it is not working properly. You need to downgrade to Msg Plus! 3.0x.
Go here:
http://www.msgpluslive.net/download/old/
If its not MSN but WLM you should try unistalling them both, Msg Plus! Live and WLM. Then delete both of their folders from your C:\ drive. Now you can reinstall and see if it works.
Hope this helps.