Strange VPC error

I have 2 PC's running in MS VPC on my Mac. The first is running XP Pro and the other is running Server 2003. Up until now everything has worked great, but now when I launch VPC I get this error:

Virtual Switch networking could not be started
Permissions for the support files were set correctly, but Virtual Switch failed to load. Please report this problem to Microsoft (Code: A1004). Virtual PC for Mac will run without Virtual Switch networking.

It didn't bother me at first because I don't even use Virtual Switch, I use the shared network function and set each PC to aquire an address via DHCP. It always worked fine before.... here's where things get strange... the Win XP VPC can still get to the internet, but the Server 2003 PC can not. Nothing has changed, they're both still using the same settings. I installed the VPC 7.0.2 patch, but no change. I restarted several times, but no change.

If anyone has any ideas, I'd love to hear them.