It could be many many things. The very first thing you should try is to reset (or as we say in computer terms - reboot) your iPad. To do this hold down the power button and the home buttons and the same time until the Apple logo appears. This will cause your device to do a complete shutdown and restart. You won't have to slide or do anything else, just hold the 2 buttons. Then after the device comes back up try the camera again. If it still causes a problem you may then want to take it in to the Apple store.