Optio S40- ON/OFF failure

Never had this problem. The last poster's idea of trying a different battery type sounds like a good one, on the theory that the camera might be getting a marginal amount of power from the batteries and wandering over and under a threshold that tells it it has or does not have enough power. If it's a low power problem, this may not be a bug at all, but a feature. The program inside the camera might have the idea that it's better to turn the camera off than to let you take a photo that comes out wrong because of power problems. Perhaps it's just overaggressive in doing that. If the power is marginal, the high drain of opening the lens might cause the voltage to drop, then when the camera shuts down again the voltage rises and the open switch causes it to try to turn on again. Following the same theory, cleaning the battery contacts with a pencial eraser might be worth trying. Another possibility is that there is a short circuit somewhere, possibly related to moisture in the camera. Is it possible to correlate the problem with humidity? If the problem is moisture related, it should go away if the camera is kept in a dry environment for a time and come back in a moist one. _Very very gentle_ warming with a hair dryer might, temporarily, eliminate the problem, indicating that it's moisture related. It could conceivably fix the problem permanently if there's a bit of water in a bad spot that needs to be driven out.

I see that the S40 uses AA batteries. I have been reading on many of these forums about the regular alkaline batteries causing "strange" problems with digital cameras. My suggestion is (if you are not already doing it) is to get some 2000ma - 2500ma NiMH rechargeable batteries and a charger. This will probably solve your problem.