For the RAW brand of CompactFlash medium, whatever you do, eject it, before you use it again. Even if you're in a hurry and even if you don't eject the SanDisk brand CompactFlash media every time, because, well, you're human and in a hurry and that still works fine, for RAW, eject it. Don't just pull it from the reader and stuff if in your camera.
Otherwise, it's almost as if the pretty rain pixie never appeared dancing in your backyard yesterday.
I know she did. I saw her. I took a picture of her. The picture might be on this RAW CompactFlash. I may never know. Because the computer can't find her. But, I'll never forget her.