My iPhone apps won't start!

Suddenly all of the apps I'd purchased and installed from the AppStore stopped working. When I tapped the application icon, the app started but was closed within a few seconds. Running the pre-installed apps worked as before.

SOLUTION: Connect the iPhone to your computer and fire up iTunes. De-Authorize your computer. Authorize it again. Make sure the iPhone is synchronized and off you go! You'll be able to run your downloaded apps again!

This will most certainly also do the trick for the iPod Touch.