I've had similar frustrations with establishing very simple VPN connections, and my recommendation is to apply Occam's razor here: the simplest explanation is most likely to be the correct one.

In other words, my first exploration of this problem would be to determine if the traffic you're trying to send through the VPN is actually going through the VPN. Check over all the advice posted so far, but first compare your results with what happens when you try to connect with no VPN. If the results are the same, then check your IP/DNS/Gateway configuration to figure out exactly how you want traffic to flow.

If it really is going through the VPN, check those ACL's very carefully and determine if all the ports you need for AD (for DNS as well as the RPC service) are supported by your VPN software/hardware.

Good luck!