Make Client Certificate from existing GEOTRUST Root Certificate

I have a root certificate from GEOTRUST (RapidSSL) and I want to make a client certificate that user need to get access for my website.

Now I have a problem to create that:

makecert -pe -n "CN=ClientCertificate"
-eku 1.3.6.1.5.5.7.3.2 -is root -ir localmachine -in "GeoTrust Primary Certification Authority - G3"
-ss my -sr currentuser -len 2048

I got an error:

Fail to acquire a security provider from the issuer's certificate

What's wrong?

The aim is an IIS Client Certificate Mapping authentication.