Cannot access VPN server after adding it to a domain

I just added our VPN server (Server 2003) to our domain (previously it was just in a local workgroup) and now I can’t log in using the a VPN connection from outside our network. I can log in using a machine on the local network and that is already a member of the domain, but not from a remote laptop (even if it is a member of the domain)

Any ideas?