multiplayer log in problem

[basset]

Hello,

I have a strange problem when playing multiplayer with a sqauad mate.

Squadie sets up a server:
I could log into him once - then after a 2nd log in attempt, I log in for a split second and lose connection. -

I set up a server:
he would log into me - but after a 2nd log in attempt, he logs in for a split second and lose's connection. -

Then he set up a server again and magically I can log into his IP again, then after a 2nd attempt, I lose connection in a split second after logging in.

We could do this all day and the cycle will continue.

Once we are connected into each others server - it runs fine, no studders, nopacket loss, it runs with 0 issues - the issue is when trying to log again the 2nd time.

The firewall is setup to let IL2 through.

Anyone have any idea what this could be ??