ssl vpn cert authentication

I'm in the midst of on how to enforce stronger security to our telecommuter users. Currently, ssl vpn users are authenticated via ldap. We want to add more security through certificate.

Already Generated my CSR under Fortigate Cert section. Followed this link https://help.fortinet.com/fos50hlp/54/Content/FortiOS/fortigate-authentication-54/Certificates.htm#Example_gen_import_CA and it gave an error which its hard for me to understand. :-). Installed as well openssl for windows laptop. I'm working on laboratory (my fortigate wanx ip address is private) first prior to configure our main fortigate which in production already.

Any help is much appreciated.