Clip Zip JPEG Limitations
It took my a while to figure out why a lot of my < 100KB album cover jpegs were not displaying properly on my new Clip Zip. I updated firmware and tried a variety of meta data tagging programs with no luck. I eventually narrowed the problem down to the image file itself. It turns out the Clip Zip does not properly decode jpegs encoded in progressive mode. (some scanners encourage Photoshop to output in progressive mode) I have to go back through and resave jpgs and retag about half my collection. (super annoying)
I hope my pain is your gain.