I have to make clear:
The Xcloner Component is ok and works well.
Actually the reason for the problem was much more simple: I am still quite new with Joomla but as far as I can say in Joomla 1.5 you have two ways to deal with a title in a list. You can set a checkbox active or just click on a title. Not so in Fireboard 1.04. If you just click on a category to create a subcategory you even delete all categories when you try to save. You absolutely have to set the ckeckbox in front of the category active to create a subcategory. This is very different from the normal Joomla way but isn't said anywhere.
Sorry for the blame, Ovidiu.
Martin