Microsoft releases a new KB (2866519) article today related to not being able to log off a RDP session on Windows Server 2008 R2. The KB article included a fix for this issue.
When you use a remote desktop connection to connect to a Windows Server 2008 R2-based computer, the Remote Desktop session may freeze, and you cannot log off from the session.
Note You can temporarily resolve this issue by restarting the computer.
This issue is caused by a dead lock situation that occurs in the Win32k.sys file…”
Source & download: http://support.microsoft.com/kb/2866519/en-us?sd=rss&spid=14134