(1) Thanks ruud for helping in my first email. This problem is solved.
(2) My second (and at the moment last) question is:
The Media Viewer isn't available in my personal wiki. The help writes, that this
feature is enabled by default but there is nothing. Making it easier for you to give me
some hints, I create a public playground with exact the same settings like my personal
wiki.
http://wiki.martinknaup.com/playground/index.php/Main_Page
I really like this feature and want it. So I need your help again. Thanks. Martin