Paid WWF Crash Fix
I sent in a help letter and was referred to this page:
http://newtoy.zendesk.com/forums/89305/entries/92302
I'll c/p in case you don't want to click:
Actually this can happen with either free or paid version and these tips apply to either one.
Uninstall both free and paid apps.
Re-download the app from the app store. Do not start it up yet. (You will not be charged again for downloading. A notification box will appear telling you that you already purchased that app and asking if you want to download it again. Tap ok)
Shut down power to your iPhone or iPod touch by pressing and holding the sleep button until the red power off button appears. Slide the button to power off.
Turn the iPhone back on and start the app. Log in using your email address / password.
Also, don't run both free and paid versions of the same app together.
If the above steps do not help perform a restore on your iPhone using the iTunes restore function.
Also note that just rebooting your phone may help too. Putting it to sleep isn't enough, it has to be a cold restart. If you don't see that red bar (see below) that lets you power down then it's not a reboot or shutdown.