You maybe changed the display setting and the game is now trying to resize into a different resolution. If this is the case, then there is a simple setting that you can change to get the game running again.
1. Launch the game.
2. An error message will appear and down in the bottom right section of the screen should be an icon of four arrows pointing outwards, tap this icon.
3. Now in the top right of the screen, there will be 2 options, deselect the 'Stretch to zoom' option
4. Don't worry if a message pops up saying that the application has stopped responding, this is normal and simply tap on OK to dismiss
5. Launch the game again and all should now be working :)