279 files can't be defragmented

I was recently working at a client site on their ancient laptop computer, which was horrendously slow regardless of whether I was working on the hard drive or the server. It did have Windows XP and MS Office 2007. I did a disk cleanup, and defragged 3 times! This didn't help; thank heavens I don't have to go there again! But out of curiousity, has anyone done a defrag with the end report stating that hundreds of files cannot be defragmented? I don't mean the "files that cannot be moved" indicated by the green bars. I mean big blocks of red bars indicating "fragmented files". I've never, on any computer anywhere, had a defrag return a report telling me that a huge number of files could not be defragmented. Do you know of any logical reason for this? Or did this horrid old laptop probably have other bad nasties going on? Thank you.