The apps may crash if the phone's RAM memory is running low. This can occur especially in the phones with smaller RAM memory, e.g. Lumia 520 and 521. To avoid the crashes, close the apps that are running in the background:
Phones with Lumia Black or later:
- Long press the back key to see the apps running in the background. Swipe through the app list and tap the X button to close the apps that are not needed.
Phones with Lumia Amber and earlier:
- Long press the back key to see the apps running in the background. Tap the app to open it and tap the back key to close it.
If you still cannot start or run the apps properly, restart the phone. You may also try to uninstall and reinstall the app that is crashing.