We've identified an issue where the latest version of the game can cause a problem with connecting to Facebook after installing. To fix this, head to your Facebook applications menu on their website (http://facebook.com/settings?tab=applications) and remove the MMX Hill Dash 2 app.
Once deleted, restart the game and connect to Facebook again to restore your progress. Make sure you select your Cloud Save. If this doesn't help, or you are having other problems please contact us using the Help and Support Link in the game Settings.