I don't know for sure... But you could check to see if hardware acceleration is turned down or off in your video settings.
I think I've had the same problem before and that was what was wrong. How my hardware acceleration/settings got changed - I don't know. But adobe flash player always seems to be involved somehow.
eta: Then again, My problem was not being able to start a game in MAME. You get that message upon exiting the game. So maybe it's not related to what I've been experiencing.