VPN failure error 800 on new XP Pro install

I can't get VPN to my office network to work on my new XPSP1 install. I get
error 800.

I know it isn't my router because other XP Pro systems behind the same
router can establish this VPN connection to the same server. The settings
on the VPN conneciton on this computer (which won't work) are identical to
those on another XPSP1 system that will work.

I have an ASUS P4C800 with built in 3 COM gigabit LAN nic thorugh a DLINK
707p router and a DSLmodem.

Any help would be appreciated.

Wilson