I'm wondering if when you copied the files from the card to your hard drive (I am just assuming that you did that), that you didn't copy the thumbnails over as well. I think I did that once with some raw images and had a similar problem. Just something that has stuck in my head from it happening, but it has been some time since that happened.

Also there is an update to the raw program available from Adobe in the program downloads area that might address this problem as well.