I've struggled with this problem also, with no results.

Comcast states that they don't filter, yet I can't get VPN to work.

I make connection to the VPN server, yet I can't Ping or Obtain NW
services.

I've opened an incident with Novell and had them connect to a test
account
on my VPN and they were able to Ping, see available port services,
etc.

It's very frustrating. I ended up making an exception in our BM
filters
for my home address to my work PC and use pcAnywhere.