Data execution prevention possibly? The files could be blacklisted from the OS for support reasons, i.e. one might muck up their system on accident with them. I've noticed some issues with Vista blacklisting some files myself though they were files that Microsoft would prefer I not use as they allow me to violate something I vaguely remember seeing in a text window about an agreement or some such s***. Turning off DEP did not resolve my own issues, but in your case it may.