I had problems with Royal TS (1.6.8) with getting the session information that resulted in a horrible memory leak that rendered my system completly unresponsive.
I was able to reproduce this with Microsoft's own Remote Desktop Connection Manager (2.2)
This behavior is related a WTSQuerySessionInformation function (from the Remote Desktop Services API) call and affects Server 2003, Server 2008 and Vista
Hotfix is available
http://support.microsoft.com/?kbid=970910