Apple will not replace hardware due to software issues, which is what you are experiencing.
Perform a "hard reset" on the device by pressing down and holding the home button and the sleep/wake button for up to 30secs. until you see a black screen with the Apple logo, then release.
Then test to see if it solved the problem, and if it doesn't help delete the app and re-install from the App Store.
If that doesn't work: http://support.apple.com/kb/HT1414