Probably, your QuickTime video can not be recognized by Creative Zen, that's because the parameter of QuickTime/MOV video is unable to satisfy Creative Zen's. If you would like to fix this problem, what you should do right now is to make your QuickTime video parameter is as same as Creative Zen. This tutorial below walks you through creating a simple extension to help you know better How to convert .mov to .avi for Creative ZEN.
In addition, if just purchased or rented one video from iTunes store, and it's unable to play on Creative Zen either, you could refer to my article of "How to convert .m4v to Creative Zen" to know the solution.
Solution to convert .mov to Creative Zen
M4V Converter for Mac all-in-one software, not only can remove DRM copy-protection from iTunes videos and songs, also can convert QuickTime video to Creative Zen video with best quality. Article of "How to convert iTunes M4V to AVI on Mac OS" will introduce you what players can play AVI video on Mac OS, Windows and Linux.
Only three steps to convert .mov to .avi for Creative Zen.
Download M4V Converter for Mac and launch it;
Click-one. Import MOV video;
Click-two. Choose output format as you required.
Click-three. Click "Convert" button to convert mov file.
How to sync AVI to Creative Zen
Drag-and-Drop M4V without DRM protection to correct folder of ZEN player
Copy-and-Paste iTunes M4V to the correct folder of ZEN player