"Q: Why do I get the error "UNREGMP2.EXE file is linked to missing export ADVAPI32.DLL:SetNamedSecurityInfoW" when trying to install the player?
A: Your advapi32.dll file has been corrupted by rogue software on your box (I believe it is now version "4.71.0118.0", which is not the version it is supposed to be). In order to fix this, you will need to go the Add/Remove Control Panel, select the "Internet Explorer" option in this list, and then run the Repair option that it will offer. At that point you will then need to reinstall the Media Player, but you should be good to go from that point."
- The WMP Mini Faq

To fix your system, you need to uninstall any prior WMP versions, expel all spyware, virus, trojans and try again. Worst case scenario is to reload the OS.

Bob