The following things may help.
- Make sure you have the most recent version of your browser and Flash Player (You might also try to uninstall and reinstall them).
- Clear cache and cookies of your computer. How to do this, is described on this page.
- Close all uploads, downloads or programs other than the ones used to play the game.
- Check your internet connection (Try to unplug and plug back your internet router to reset the connection).
- Try to connect to the game with a different browser.
- Try to connect to the game from an other computer.