Windows 7 VPN Error 766

I tried to reinstall my windows. Now I have two user accounts. One of them can coect to a VPN while the other caot. It is really strange... It gives the error 766 listed below.

Coecting to vpn.cuhk.edu.hk using 'WAN Miniport (L2TP)'...

Error 766 : A certificate could not be found. Conenctions that use the L2TP >protocol over IPSec require the installation of a machine certificate, also known >as a computer certificate.

Anyone knows why they are different in two accounts? Any suggestion to work on?

Thanks.