Returning to my office after an absence of 3 month, I started the database
front end Rekall, and it worked fine.
After this I downloaded and installed all available upgrades.
Thereafter, Rekall did no longer work. It was broken. I assume it needs a
re-compilation to bring it up to date again. 
There are other computers in the office that experience the same problem.
I tried to fix matters by re-installing the software from the repository, but
to no avail. 
Thanks for a timely attention.