Thank you for the fast reply.
I already tried this. I went through all available menu settings.
There seems to be a bug in the top right menu.
I have deactivated the Under Construction Plugin for 48h so you can take a look.
http://pb-tietz.de/?page_id=28
When you scroll down u can see that the top right menu is still sticking to the top of the browser window, but there are no menu items. I have set the same menu for top right menu and the secondary menu which is visible.