I already tried to Make sure Messenger is shut down and closed.
Then Click "Run"
Copy and Paste this " regsvr32 MSXML3.dll "
You should see a dialog box stating that the operation has suceeded.
Then open Messenger again and sign in.
If this doesn't work then try to clear your DNS cache by:
Click "Start" then "Run" and type "cmd.exe"
Then type "ipconfig /flushdns". You should get a message stating that the cache has been cleared
And Microsoft support isn't helping.