I figured out that the small browser inside ZMI has a problem with javascripts, it can't display them. But, when I visit the URL of the page from IE, the javascripts are executed normally.
Now I understand why this fails. You are pressing the View/Test tab inside the ZMI. For some objects, zope will add an extra text at the end of the url. ie: for images it will add: /your_image.gif/view_image_or_file, for scripts, page templates, and other objects, it will add /your_object/ZScriptHTML_tryForm. For other objects no extra text will be added, so they will work as expected. (Look at the status bar of your browser before hitting this tab).
Am I right that ZMI can't displays JS ? and is there a solution for it. If I'm right, this is a path problem, one could solve it, but I think the invested time isn't worth. You'd better copy and paste the link from the View/Test tab and remove the extra text at the end.
Regards Josef