Right-click on the Computer icon and go to Properties. If you're using Windows XP or below, go to Advanced. If you're using Windows Vista or above, go to Change Settings and click the Advanced tab. Press the Settings button below the Performance, click Data Execution Prevention and check the second box. Click the Add option, navigate to the game folder, select the Splash (executable) file and click OK. If this doesn't solve the problem, I suggest you download and install the latest version of the client from the official web page. Be sure to uninstall your current version before installing the new one.