It works on the demo site.
I can't see any java error. How i can find any errors??? A tool?

Are you using Firebug? If there are any errors, it should be reporting them in the bottom of your screen.

I installed firburg. It says:

fire(Object { name="element"}, Object { name="eventName"}, Object { name="memo"})prototype.js (Zeile 3972)
_methodized()prototype.js (Zeile 246)
fireContentLoadedEvent()prototype.js (Zeile 4006)
[Break on this error] element.dispatchEvent(event);

and maybe u know what that means:

$(this).parents("div.datepicker:first").metadata is not a function
http://www.tresenwald-volleyball.de/dataobject_manager/code/date_picker_field/datepicker_init.js?m=1282690421
Line 5

$("a[rel=clear-btn]").live is not a function
(?)()datepi...2690421 (Zeile 9)
bindReady()base.j...6521538 (Zeile 503)
bindReady()base.j...6521538 (Zeile 503)
each(Object { name="object"}, Object { name="callback"}, Object { name="args"})base.j...6521538 (Zeile 336)
bindReady()base.j...6521538 (Zeile 503)
[Break on this error] $('a[rel=clear-btn]').live("click",function() {

uncaught exception: XBL binding for <button type="menu-button"/> binding must contain an element with anonid="button"

Line 0

nobody can help me???!!!

Uncle Cheese ??????

Nobody on world can help me? Plzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz

I really don't know.. if it's working on the demo site for you it must be your installation. Do you have any other Javascript plugins that might be conflicting with it? Are you running the latest version of EventCalendar and Silverstripe?

I work with the 2.3.3. Maybe that is the reason.

Is a upgrade to the latest version complicated?