I had a funny problem and finally solved it, maybe it could help someone here. This morning, I was using my K3 with my new (very old) SMC 135mm f2,5 fully manual lens. I was using the green button to activate the meter in full manual mode, Most of the time, the camera completely froze and even removing the battery didn't help. The only way to make it work was to select MF on the focus selection knob on the left side. Leaving it at the AF position made the camera freeze. Anyway, the lens IS manual focus. Now all is working fine. Here is a sample taken with this fine lens.