That really helped,
and some of my commands are now working as intended ... but ... others not yet.
I prefer working with one lage viewport therefore I want to set up my numpad in a way,
which makes it possible to access every view. Usualy I use em the following way:

0 = 3D View
1 = Bottom
2 = Front
4 = Left
5 = Top
6 = Right
8 = Backview

The views 3D, front, top and left work,
right, back and bottom do not. I already tried to add
a Ctrl prefix, like you have to use it when you klick
the view buttons, but with no result ...
What do I do wrong here?
Regards
Heiner