Insufficient memory could be the culprit. As applications are launched and closed throughout use, more and more of the system's memory becomes occupied. Removing unnecessary apps from the multi-task bar and then rebooting your device before play should resolve your problem.

You may remove apps from the multi-task bar and free up additional system memory through the following procedure:

1. Double click the Home button, located on the bottom center of your iPhone.

2. The applications currently running in the background will be displayed in the multitask bar running across the bottom of the screen. Touch and hold an icon until it begins to shake.

3. Icons will be displayed with a minus (-) icon in the upper left corner. Touch each icon to fully close the app. (These applications will NOT be deleted from your device.)

4. Press the Home button again to close the multitask bar.

After completing the above steps, please try rebooting your iPhone and then launching the game again. We expect this will resolve your difficulties, but please let us know if you continue to have trouble.