Is it synced with an online service like iCloud or GMail.
If so, try going into the account's settings and turn off Contacts, choose Delete when it asks if you want to Delete or Keep the contacts. Open the Contacts app to make sure everything was deleted. Then go back to settings and turn your contact syncing on again.
Do this only If you are syncing your contacts and know that the database on the server is up to date.
Here is the list of usual fixes anyway, just incase you missed one.
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When you have problems with an app it's a good idea to clear it from RAM.
Close/Clear the app: With the problem app closed, double tap on the Home button to get the multitask bar. Tap and hold on any icon in the bar until they jiggle, then tap the minus sign on the problem app. This will remove it from RAM and insure a clean start the next time you launch the app.
If that does not work try a restart,
Restart: Hold down the power button until the power off slider appears. Slide it off. When the iPad finishes shutting down, hold down the power button again until the Apple logo appears.
and then a reset if that does not work.
Reset: Hold down the power and home buttons until the Apple logo appears. The iPad will reboot. This usually takes a bit longer than a restart.