this is what i did: i tried to play a .mov file withWMP without having any codec for that installed. wmp opend and gave that popup with " extension is unsupported but that it may be able to play it back anyway". at this point i capture the registry. then i check that checkbox and capture the registry. this is what i got: HKCU,"Software\Microsoft\MediaPlayer\Player\Extensions\.mov","Runtime",0x10001,1 HKCU,"Software\Microsoft\MediaPlayer\Player\Extensions\.mov","Permissions",0x10001,1