When connecting to the web enrollment page for Windows Server 2003 Certificate Services from a Windows 7 or Windows Server 2008 client you may encounter this warning message.
The certificate enrollment page you are attempting to access cannot be used with this version of Windows. To enable Web certificate enrollment for clients running Windows Vista, your administrator must update all Windows CA Web enrollment pages.
This is due to an ActiveX control used by the web enrollment pages that has been deprecated in Windows 7 and Windows Server 2008.
To fix the issue install this hotfix from Microsoft on the Windows Server 2003 server that has Certificate Services installed.