IPhoto 8 won't import jpg's - unrecognized format

Question

I am not able to import some jpg's into my MacBook. These are on a Xd card from my camera. I've been able to import photos from there as recently as yesterday without any problem at all. They are vacation photos so they are very important.
I'm using iPhoto 8.1.2 on OS 10.6.3. When I try to download my 180 photos or so, THREE of them import successfully, but the others are rejected. A pop-up window tells me that they can not be imported because they are a unrecognized format.
When I try to open those files in Preview, I also fail to open the jpg's. My Finder window detects them as a jpg, but I haven't found anything yet that will open them.
Any help would be appreciated!

Answer 1

Here are my comments about your other worthwhile comments:
"Consider using these best practice tips to avoid or minimize the impact of issues in the future:
_Ensure your camera has a full charge on the battery before you import (Or run off of AC if possible). {YES. I keep a full charge on the batteries at the start of every photo day and I did on this one too.}
_Ensure the date and time on the camera are correct before importing. {YES. It has been correct and remains so.}
_If you are using a media card reader and are getting regular failures, try using a different reader or the camera itself (The same is true about importing directly from the camera. Try a reader instead.) {I do use a card reader. It has always worked like a charm. Using a Digital Concepts model.}
_Plug the camera directly into the computer with a solid connection, no loose cables. Don't use a hub. {I will do that next.}
_Reformat the camera's media card using the camera itself between uses. {I normally do that but didn't this time. The manufacturer also recommends reformatting after EVERY use.}
_Alternate between multiple media cards during photo shoots (trips, etc) so that if one card goes bad (they are just little bits of plastic after all) you don't lose the entire shoot." {I'm likely to do that more often now. I keep three cards just in case.}
One more thought. My camera (an Olympus SP-560UZ) actually has problems every now and then using Alkaline batteries (even the best ones). It encounters a "zoom error" when turning on. The fix is to use PREMIUM rechargeable batteries. I had a hard time believing that one. But I tried the better batteries and it does make a difference for the better. They usually last me for six hours or more of keeping the camera powered; an important aspect when I'm hiking in the mountains and need to be prepared for anything.