Hi,
...solved.
of course I needed to downgraded to php 5 in order to be able to run
Moodle 2.9. The point is that I upgraded the Debian from 8 to 9.
The php 5.6 packages were still installed in Debian according to aptitude
although the current php-comand is linked to php7.
Non-the-less I had to reinstall it. I needed the packages from ondřej surý.
Now it works ...
... wish you a merry Christmas and a happy new year!
Best,
Fab