Try this:
Go to settings, apps, go to all, open "Camera" and press "Clear data".
Now try again and see if the problem still persists.
If the problem persists, we recommend you to download the Sony PC Companion and you can repair the phone software:
Click on this link to get Sony PC companion:http://www.sonymobile.com/gb/tools/pc-companion/
Start PC companion, start "Support Zone", start "Update phone software" and click on "Repair".
Follow the on-screen instructions.
