another cause for the error is the newish update to avg anti virus from 7.5
To disable the problem
1. start AVG and select - Tools - Advanced settings...
2. then open the web shield icon on the left pain and select Instant messaging
3. finaly untick the msn messanger tick box and click ok
no need to reinstall or uninstall messanger just start it up and sign inas
messanger should then work - or did for me