I don't know if this has been answered yet but when i try to start the game in campaign more i get about 1 sec. into the opening video then the game stops and i get a gray screen saying "Error initializing network layer".

This doesn't make sense to me cause I'm trying to play offline as it is. I can play the levels through "Instant Action" mode but when i try to start a new campaign it cuts out at the same point.

Hardware:
ASUS M3N78 Pro AMD MB
AMD Athlon 64 X2 6400+ (3.2 Ghz)
4 Gb of RAM
On board network card
Nvidia 7800GT
Windows XP 64 Bit