XP PPTP VPN & Netopia DSL Router

I am trying to set up a pptp vpn connection between an XP server and
either an XP client or a Win2k client (the latter for test purposes).
I have done this successfully with a Win2K server and Linksys router.
But now I am having connectivity problems.

I set up the XP server according to tutorials provided by others on
these forums - and I believe I have everything done correctly. I poked
a hole thru the firewall for port 1723 and protocol 47 (GRE) for a
static LAN addressed XP server machine on the LAN. I restricted the
range of DHCP to stay away from that static LAN address for the
server. I hardcoded the static WAN router address in the vpn client. I
can ping it successfully.

I get Error 678 when I attempt to connect. Can someone point out what
is wrong and provide some trouble shooting references.

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