Hi, I have noticed that(almost) every time I try to play a game a small message will appear that says "Could not open file (game)". I have also found that if I push the Back button and go to the previous screen and then push the Forward button I am able to play the game.
That has never happened to me, and I have been on the site testing it a lot. You may want to try switching your browser, and making sure you have the latest version of the Flash Player.