Optio E35 - Cannot forma SD memory cards

I've just received a Pentax Optio E35 as a gift. I tried it first taking some shots with the internal memory, and then of course I inserted an SD memory card. With my surprise, I was not able to format the SD memory card. I tried with two different cards (Panasonic 512MB, San Disk Ultra II 1GB), but no way. I followed exactly the instructions, but when I start the Format process, it just show the message "Data being processed" for a few seconds and then it stops with the message "Card not formatted".
The two cards where previously used with a Panasonic camera (which does not require to format the memory card anyway).
Did anyone experienced the same problem?