With my iPad that is usually indicative of too much current RAM memory. When it happens to me a hard reset clears the problem without any further issues. Hold down both the on/off button and the home button until the screen goes dark then the Apple icon reappears then release both buttons. You should be goood to go.
If the problem keep happening back up your iPad to your computer then delete all information and settings (go to Settings--General--Reset--Erase All Setting And Content) and restore the iPad from new as the problem could be the in the iOS software.