Thanks for the reply.
I've just had a look through the links and found no solution.  The crazy thing is that I have had pptp running great on a 6.0b3.  That is why I recommended it to my customer in this instance.  
The working solution was a new install however, this one is an upgrade from 5.6b4.  Both are working in gateway mode.  The other one is also setup for PPPoA with a PCI modem, this one is working via another ethernet gateway (my customers network provider) and a standard ethernet card  - maybe that could make a difference???
I am going to try my luck with the IPSEC contribs and a Safenet Softremote client.  Hopefully that will work.
Thanks again,
Chris