Proxy Server and WAN

I am running MS Proxy Server 2.0. Clients on the local network connect using the WSP Client with no problem. I haven’t been able to get the client to work across our WAN. The WAN is a frame-relay network using Cisco Routers. The LAT is configured onthe Proxy Server for the remote subnets. I suspect there is a configuration entry I need on the routers. Any ideas?

Thanks for your help.