iPhoto: Unreadable Files

Hey guys, I opened iPhoto today and found that all of a sudden there aren't any photos inside it. I checked my iPhoto Library folder and they are all there still. They also still transfer over to my iPod. I tried dragging the whole iPhoto Library folder into iPhoto but I get an error message that tells me there is an unreadable file and they cannot be imported. I also tried just dragging one actual .jpg picture into iPhoto but I still get the same error message. I searched around and tried rebuilding my library but when I click Ok, nothing happens. What is wrong here?

Hmm weird, I dragged my Data folder with all my actual photos in it out on to my desktop and then dragged it to iPhoto, and it imported them all fine. Is it working now? What caused this?