A bit more on this. Microsoft has been steadily doing updates on version 9.0c Direct X. Latest is November 2008 (which 8 L.E.I.N.'s link leads to). So even though they kept the same name and version number, it's different. Suggest you download the "Redist" version and keep it in your backup files.
<editorial comment> Great way for them to push DX10 sales, eh?