Does this mean that Flash Player works well at other sites? If the problem persists only with a particular site, then it might be that it is not a Flash Player issue but a requirements issue (your system vs the game requirements).
Anyways, assuming that you have Flash Player issues while browsing multiple site, first find whether your system meets the minimum requirements: http://www.adobe.com/products/flashplayer/tech-specs.html
Then find if you have the latest version of Flash Player version: http://helpx.adobe.com/flash-player/kb/find-version-flash-player.html
Use this document http://helpx.adobe.com/flash-player/kb/installation-problems-flash-player-windows.html to find a solution.
Hope the above helps you.