Using RDCMan v2.2 build 2.426 downloaded from http://www.microsoft.com/download/en/details.aspx?id=21101
Client is Windows 7 x64 SP1
Servers vary from Windows Server 2003 R2 to Windows Server 2008 R2 with same result
Error message when attempting to logoff a session either individually or as a group:
"Unable to log off from [servername] Reason: Unable to enumerate remote sessions."