I keep getting "CD Key in use by Battle.net" error

My cousin and I both purchased and downloaded the Battle.net version of WCII this weekend in an attempt to play online together. After doing the port forwarding, one of us ALWAYS gets the red “CD key in use by Battle.net” error message. I’ve submitted a ticket and the support “Game Master”’s answer was to send me to this forum. It’s sad that we care more about the games than the people getting paid to!

Any help is greatly appreciated. I work as an IT professional, so all of the usual things have been done. Even leaving a PC off all night doesn’t stop the error at times.

It helped me to turn on the VPN, and set up the router manually, transferring ports