try to get DER version, see 2.j and below in".... j. Click Next, select DER encoded, and then click the Download CA certificate link. Save the certificate file to your Web server's local drive, and close your Web browser. ..."HOWTO: Set Up SSL Using IIS 5.0 and Certificate Server 2.0 http://support.microsoft.com/default.aspx?kbid=299525 also see http://support.microsoft.com/default.aspx?kbid=290625
j. Click Next, select DER encoded, and then click the Download CA certificate link. Save the certificate file to your Web server's local drive, and close your Web browser.
..."HOWTO: Set Up SSL Using IIS 5.0 and Certificate Server 2.0
http://support.microsoft.com/default.aspx?kbid=299525
also see
http://support.microsoft.com/default.aspx?kbid=290625