Certificate Retieval Failure ‘80090024’

I have users who need to retieve a certificate from an external web site. When they go to retieve the certificate they get an error in a box titled – VBScript:Internet Explorer Certificate Request inside it states: The error ‘80090024’ occured. Your certificate request could not be generated. The users having trouble all belong to the same active directory group. Our active directory server is running windows 2000 server. If I log on to the same machine (windows 2000 workstation)as someone in another group I can download the certificate.

What setting have I used to prevent this group from getting a certificate.

Thank you