Vanishing album art

I've been looking for a program to help me organize my music collection and after much searching came across Mp3tag, which looked like it just might be the answer to my prayers. The program has been awesome for organizing all tags and filenames, but when it comes to assigning album art, not so much unfortunately.

The problem is that the album art I embed using Mp3tag doesn't show up in Winamp or in my mp3-player (a Creative Zen Vision:M) which makes it pretty much useless. I would really like to know if there's anything I can do to fix this or if someone knows a way of getting around the problem? I had the exact same issues when I tried using MediaMonkey to embed art, and I really hoped that Mp3tag would be the answer. Right now I'm stuck with adding a .jpg file to every album folder to get visible album art, which sucks since I can't add art to any of my random album-less mp3's.

EDIT: Apparantly some of the art I've embedded shows up in Winamp and on my Zen, while some does not. Can anyone explain this?

I can't explain this (because I'm neither use Winamp or have a Zune) but have you tried to removed the files from the library and add them back again after adding/changing album art?

Also make sure that you write ID3v2.3 tags with UTF-16 (you can edit this option via Options > Tags > Mpeg).