XEnroll Api - ICEnroll4::addAttributeToRequest

I am trying to create a certificate request with additional attributes using XEnroll api on XP (as CertEnroll is not supported on XP), I am calling:

(1) ICEnroll4.addAttributeToRequest (to add an attribute)

2) createPKCS10/createRequest (to create a request).

but I donot see my attributes getting added I only see default attributes.

I was able to addAttributes using CertEnroll api on Windows7/Vista. But I need to support XP also so using XEnroll api.