You could try a
System Restore.
Otherwise, check which applications you've got running that could cause conflict.
Do you have any Messenger add-ons? Uninstall them all (SweetIM, SmileyCentral, MessengerDiscovery, etc.) as well as Messenger Plus! Live, just to be sure. Then restart Messenger and see if the problem still occurs.
If still no luck, run your computer in "Safe Mode (with networking)". Instructions
here. Run WLM, see if the problem occurs. If it doesn't, it's most likely that an application is running when in normal Windows mode that is causing the problems, which you'll have to try and find.
/ 
