I haven't heard of anyone having this problem before.
First thing to try: restart the device. To to this, hold down the power button, then "slide to power off". Then hold the power button to turn the device back on. Now try the game again.
If that doesn't work:
1. What game is this, the original Tasty Planet for iPhone, I assume?
2. What kind of device are you playing on: iPhone 1, 3g, 3gs, 4, 4s, iPod Touch, 2nd, 3rd, 4th, iPad, iPad 2...?