certificates

Hi to every one !!
i am trying to create a certificate from a standallone CA for L2tp/ipsec .i know that to take a certificate from a Ca standallone can be only by the web interface of the CA .

i request the certificate and install it succesfully but when i try to connect to my VPN (Ras ) server i take the error “798 A certificate could not be found that can usedwith this extension authedication protocol”

can any one help on this ?