I'm having trouble with Source Filmmaker

It said in the update I now have Beta access but when I click "click to install" it says "Source Filmmaker is not available on your current platform". Do you guys have any idea what this means? I'm refusing to exit out of it or close it until i know why. I don't know if I can get it back or what so I'm leaving it alone until later. So yeah again do you guys have any idea what this means?