On May 9th, 2009 Entrust Managed Services (provider of HSPD-12 certificates) performed a key update ceremony on the Entrust Managed Services Root and SSP certification authorities. HSPD-12 certificates issued after May 9th, 2009 will not work on the Windows XP operating system (i.e. RTM, SP1, SP2 and SP3).

More information can be found in the Document HSPD-12 Logical Access Authentication and Active Directory Domains.