I have added 2 root certificate using the control panel from StartSSL. It use RSA. After import the certificate appears in my list and I confirm their information using the view button.
However when I try to connect (thru my application) to our test server requiring those certificate, it fails on HttpOpenRequest with the GetLastError() returning 0x80091004 (CRYPT_E_INVALID_MSG_TYPE).
I don't find that rsabase.dll actually exists, even though that page references it. Instead, I beleive that rsaenh.dll implements the RSA support. Rsaenh.dll is included in 5.00.27 GCX_Core.