Firewall Clients

billybob01

I am having difficulty working out why our Firewall clients are unable to automatically connect to the ISA 2004 Server. They can only connect manually. I have configured the settings in the properties of the default Firewall Network and i have enabled Auto-Discovery Publishing on the ISA Firewall Network. WPAD has been setup in DNS and all other setting appear to be correct. I have run the ISA Diagnostics and found an error that might relate top my problem.
Event ID 30042
Packet Context 0000702f
Source does not match the packet.
Any ideas of what i can try next as i have hit the preverberal brick wall.

The Auto-Discovery port is set to 80 and we only have the one Domain.