My A 100 camera developed the same error a few months back. First it was in 30-40 percent of cases, slowly the frequency increased especially when attempting distant focuses, and finally all outside (full light) attempts. It was alright in indoor operations. I gave it to Sony workshop for repair (warranty has elapsed). They kept the camera with them and then reported back (in Delhi) that camera can't be repaired and they will replace it with new unit at Rs. 20000 (this is 10 mp camera, a new 14.2 mp camera is available for around 19,500). I had to take back my camera back. Today I tried several options before discarding it, and found that if camera is set to minimum aperture stop (f 5.6 with my normal 18-55 lens, f 4.0 with Minolta AF Zoom 35-70 lens) I was able to take photographs in both AF and MF mode, and even Macro mode, even close ups with extension tubes also gave good results. I have not tried it much, but appears I don't have to discard my camera any more.