Canon S3 lost my pics

[digime]

Please help me solve this one: My Canon S3 has performed flawlessly for over a year. This morning I shot my daughter's softball game on a SanDisk 2gb Ultra ll SD card, both pictures and video. I downloaded them using SanDisk ImageMate 8 card reader into my iMac. So far a typical shoot. I then went back for the opening ceremonies and took several more shots. (No reformat on the card, just added more shots like I've done several times before. Now when I try to download the other pics and video do show up, as if they were never shot at all. A few of these pics and video were shown to other people on location, so I know they were shot and played back just fine. But now, no new pics at all. How could this happen? I've never had a digital camera that dropped all new images shot. I'm not crazy but I probably will be if I don't get those pics to show up. Thanks for any help you can give.

[alexphotos]

get lexar image rescue or the scandisk one they car read all the information on the card.