if allready posted somewhere...my excuses, i couldnt find it

I installed fsx on my machine and it works like a charm, even so that my wife wants it too :p
So another fsx brought in and installed on her machine... But now it comes. I cant logon to gamespy or connect to flights hosted by my computer on her computer. If she looks in multiplayer it says either you are logged on on another computer (gamespy) or you dont see the host session on my machine.
If I make a host session on her machine, it does showup on my machine put after clicking on it it will not proceed.
As a test I installed fsx on a 3rd computer. From that machine all works again like a charm and every connection between taht machine and my machine is perfect. The problems with connecting to my wifes computer stay the same

All three machines have vista on it and are connected through the same local network. I thought about a firewall issue on her machine, but disabeling didnt give any result.
Yesterday I saw on a ms site the same problem started in a thread there, but no answer yet and i doubt if one comes since there is hardly one active where he posted

Any suggestions?
regards,
Bold