Which browser are you using? I've copypasted your code into a fresh branches/2.4 installation, and the calendar shows up fine when clicking into the field (both for ajax load and when the form appears directly on a subsequent browser refresh). I don't think browser cache should have anything to do with it, but I've disable cache completely during testing just to be sure.

thx for response...
Its not browser issue does same with all browers. IE, FF, Chrome.
And funny thing in this is that this works fine on my local wamp server but not on my customers lamp server.

I did some test without Datefield cause i noticed that dataobject manager module does behave similary. After first load it just dosnt show as it should be (clean mac like title bar with text displaying 0 to 0 of 0)... AND when i try to add new Dataobject it goes to URL in main browser window while popup should appear.

BUT everything ok after refreshing admin site.
Tryed this with clean installation with silverstripe 2.4.1 and dataobject_manager 414.

This is realy weird stuff. Any idea everyone what could tie silverstripe, javascript and server together.