Are you using Windows Live OneCare? if so, open OneCare, click change settings, firewall tab, advanced. Go to the Ports and protocols tab and click add. Enter a name for your rule, enter the port range as 4277 to 4277 and select UDP. The scope would be inbound and outbound. (I'm giving you the steps from memory, so some of the wording may be different on the add dialog).
If that doesn't work, please contact OneCare support.
How to reach support (FAQ) - http://social.microsoft.com/Forums/en-US/onecareinstallandactivate/thread/30400b52-7f26-4ba0-bc18-17e305329d90
-steve
Microsoft MVP Windows Live / Windows Live OneCare, Live Mesh, & MS Security Essentials Forums Moderator