HI Devid,
Did you upgrade the MSXML 4 (SP2) or it's a fresh installation?
If you wish to reinstall, first take systemstate backup so that if any thing went wrong you will be able to restore the DC. Do you have Additional DC in your environment?
also follow the microsoft release note to upgrade or reinstall the MSXML 4 (SP2).
http://download.microsoft.com/download/9/6/5/9657c01e-107f-409c-baac-7d249561629c/MSXML4SP_RelNote.htm