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Does this happen all the time or with flash only?
Do you have a phone case installed?
Did you check if there is dust on lens?
These tips where for the issues Xperiam2teng where having. I would recommend you, cis124 , to start a new thread if you do not have the same issues are Xperiam2teng as I can't say if these tips are applicable for your issue.
No, you need to do it once, if the camera keeps stop working after this I'd suggest that you do a PC Companion phone repair, this will do a clean installation of the latest firmware and will also wipe your internal memory. Don't forget to back up your data before you proceed.
Open PC companion -> Support zone -> Phone/tablet software update -> Repair my phone/tablet (blue link style). Follow the steps given, do not connect your phone until prompted to press volume down while plugging USB cable.
http://www.sonymobile.com/gb/tools/pc-companion/