WINXP VPN Server error 733

Hello Everyone,

Following Problem that has been posted before but i never found a post
with a solution.

following scenario: WINXP Pro should work as a VPN server. A friend who
helped me testing to connect to the VPN Server from outside my network
over my router always got the error message "733" while he was trying
to connect.

To make sure that no Router-Port-Forwarding-whatever-kind-of-problem
accured here i tried to connect inside my network from a WinXP-laptop
to the WinXP-VPN-Server. And the same Error message appeared (733).

To check my settings i configured my Laptop with he exact same settings
as the other WinXP Machine. i could connect inside my Network from the
other machine and also my friend could connect over the internet after
i forwarded the ports to my laptop.

i tried all the basic stuff (put off firewall, rebootet without any
programs in "start up" (also in msconfig) etc.) but didnt find a
solution yet.

the settings seem to be allright so far because i double checked them
with my laptop where everything worked fine. i have no problem
with my router/port forwardings. i just have a router with one machine.

Did anyone have the same problem and found a solution?

thank's in advance for all answers,

regards, Christoph