listening client only gets gray screen- but mouse moves

[Johannes Kutsam]

 I have a ComputerB behind a Firewall that i cannot change and a 
 ComputerA behind another firewall both run WindowsXP.
 B is running a VNCServer. A is running the VNC listening client.
 The Firewall at A's network is configured to forward 5500 to A.
 When B add's A with "add new client"  the following happens:
 
 a VNCVIEWER window pops up however it stays gray. If A moves the 
 cursor however it really moves the cursor of B, even though A does not see
the mouse cursor rendered - just the small square.
 
 I wonder whether VNC is using any other ports to communicate.
 I have tried this scenario twice. Once with B and A and again 
 with a computer similar to B in another network (C and A) - the result 
 was the same.

Could it be related to the vnc hooks, or fast user switching?


(I am using VNC 4 - built on june 15. 2004 )

 Thanks for any help,
 
 johanns kutsam