Sorry, for coming back so late.
First of all, thanks for your tips, Kovid and itimpi. I play around the different possibilities and had success in both ways.
At the end Kovid's hint to the special note was the eye opener, I was looking for. Sometimes it is realy tricky to find the right information in the helpfile (I am using it quite often). I had after deleting the old book and import of the index.html a new zip file, which is after converting to an epub in the correct reading order.
Now I will play a bit with the toc generation and have at the end of the day hopefully a nice sample project for Calibre
