I keep getting this on my phone. I just got it as a replacement 5 days ago.
You may need to reset it. While a hard reset deletes all your information, you can clear the system cache which does not erase any personal data or settings. This feature allows for clearing of all application/background "cache" .
To clear the system cache to reset the phone, follow these steps:
Watch this video to get a better look. http://www.youtube.com/watch?v=2obtfreghtY
Only slightly different with the same effect.
Check out a fun infographic that teaches you how to increase storage, enhance security, improve battery life and clean your device.