Dear Stefan,
We figured it out. It was very simple. On the table in the first page that gave us a problem, I went to the last row on the page, the leftmost cell. This one could not be edited. I went to the next cell to the right and for some reason it was editable and pressed the enter key to add a line. Wunderbar! The cursor entered the leftmost cell and it worked.

As instructed, I repaired Office 2007.

Danke,
Alles Gute
The way you spell your name, I assume you may understand German.