Chosen Solution
After about six months my T2i flash quit popping up. The camera makes a clicking sound and then gives me a 05 Error saying that the camera should be turned off and back on but it has never reactivated.
There is always a rusted screw found under the top cover of flash, which has spring to move the flash head. By unscrew and cleaning it (filing ), solves the problem from its root.
Try this..
