Setup of VPN using certificates with XP upgrade

Has anyone successsfully gotten this to work?

I'm attempting to set up remote access for users in our
office, through our RRAS server. I've gotten successful
VPN connection in the past with a clean install of XP
Pro. I requested and installed an IPSec certificate, all
that.. I just tried it with an XP Pro box that was
upgraded from Win 98 and I'm getting Error 786 "There was
no valid certificate found on your computer".. I know
there is a certificate there, I'm looking at the $%#@
thing.. Any ideas?

Thanks in advance...

Kathleen