optio s4 pictures unreadable on computer

Hello, I just bought this camera and an 256SD memory card for it. I tried the card out when I first got it and the pictures came up on the computer under the removable disk drive then DCIM then 100 Pentax file. Now the pictures that I have on the camera are viewable but when I double click on the DCIM folder it gives me an error message. I don't know what to do.

Any advice would be great
Mike