When you don't log off Windows Remote Desktop (or terminal service client), the connection becomes
orphaned. You may get the following screen:

Too many sessions prevents future logins.  Do the following to clean up connections (on Windows 2003 server). 
From a client machines CMD windows:

D:\>query session /SERVER:myserver.myco.com
 SESSIONNAME       USERNAME                 ID  STATE   TYPE        DEVICE
 console                                     0  Conn    wdcon
 rdp-tcp                                 65536  Listen  rdpwd
 rdp-tcp#11        Administrator             1  Active  rdpwd
 rdp-tcp#4         Administrator             2  Active  rdpwd

The above show 2 connections to "myserver". You can kill the sessions with ID 1, 2, 3, so on.

tsdiscon 1 /SERVER:myserver.myco.com

where 1  rdp-tcp#11        Administrator             1  Active  rdpwd "ID" col
Also, can tskill to remotely stop a process