I have had this problem too. Here's what I did:
1. Delete the app.
2. Completely shut it down. To do this you:
a)Press the lock button for five or six seconds.
b)When you can see a "Slide to Power Off" switch, slide and it will
completely shut down.
c)Reboot it again by holding the lock button again for five seconds.
3. Now re-install the app.
It worked for me, I can only hope it worked for you!