For those having problems upgrading to Messenger build 566

messenger%20buddy News
Here is a little tutorial on how to overcome some problems which occur while upgrading from build 562 to build 566 of Windows Live Messenger from Microsoft Connect (with permission from the Beta Team):

 – Run Messenger 8.0.0562
 – Attempt Signing-in, get the Upgrade prompt (1st upgrade prompt), says YES (to upgrade) and go through the full installation wizard
 – Attempt Signing-in, get the Upgrade prompt (2nd upgrade prompt), says YES (to upgrade).
 – Now, a Repair Remove dialog will be displayed.
 – If user chooses to REMOVE the client, the client shows removed in the ARP but there is still a client running on the machine
 – Attempt Signing-in, get the Upgrade prompt (2nd upgrade prompt), says YES (to upgrade) and user will be walked through the full install wizard.

Or you can simply uninstall the old version and run the new setup, for technical details look at Jonathan Kay's space post.

I know that it's a pain, but this is a checked and documented workaround for the issue. Hopefully this clears up any problems you may be having with the upgrading. Happy IMing! :)