Hi MJT –
I think I may have an idea of what is going on. Without going into too much detail, the gist is that you’ll want to check out ALL the shortcuts that point to Messenger, and make sure Run as Administrator isn’t checked. You’ll also need to go and do the same on msnmsgr.exe directly.
First, check the shortcut on your taskbar. Right-click on the icon, then right click on ‘Windows Live Messenger’ -> Properties -> Compatibility -> Privilege Level. You’ll also want to do this on the Start Menu shortcut, the Desktop shortcut if you have one, and any others you can find.
Then on one of the shortcuts, click ‘Open File Location’ and then right-click and change the compatibility settings on the msnmsgr.exe.
Let me know if that helps.