Sticky: FSPortTest - network test tool - check your network setup

Hi Russell. You've probably covered this but I missed it.
My problem:

I've set up FSHost and tested port forwarding using FSPortTest. All ports test fine.

I can connect to FSHost with FS2004 running on the same machine using port 23455, however when a friend tries to join FSHost on port 23456 after I have, FSHost says he has joined but is "not in aircraft". His FS2004 hangs for over a minute and then FSHost reports a disconnect.

Conversely, he can connect properly if he goes first but when I try and join with FS2004, it hangs and FSHost displays the 'not in aircraft' message followed by a disconnect.

We've both joined other FSHost servers and not had any problems but I don't know if the host was using FS at the same time or not.

Thanks for any insight you can provide,
GeorgeH