I have been experiencing an issue with a Cisco VPN Client while connecting to a government site. The problem began occuring when we moved the workstation that it is on to a new domain. Once on the new domain we could not contact the site (our connection would fail).
If I move the workstation back to the old domain, the user can connect to the site via the VPN no problem.
I believe that it may be a DNS issue. Our old domain was a NT 4.0 domain controller and the new one is an Active Directory domain. Prior to the new domain our DHCP would point users to the ISP's external DNS, because of AD the new DHCP points to the internal DNS which is also the AD server.