Try this - Reset the iPad by holding down on the Sleep and Home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons. (This is equivalent to rebooting your computer.) No data/files will be erased. http://support.apple.com/kb/ht1430
Troubleshooting apps purchased from the App Store
Delete the app and redownload.
Downloading Past Purchases from the iTunes Store, App Store and iBooks Store