VPN – Domain not available

I setup a vpn between a cisco pix 501 and a cisco vpn 3005 concentrator. I am able to ping through and even can log in a user who has logged on before. However when I try to log on a machine I haven’t before it tells me that the domain is not available.

I tried lengthing the time it waits for a response in the registry, it just took longer to give me an error.

I am wondering if it is because the workstation and the server are on different subnets? If so how do I get past this?