Solved: Kernel error message at boot time
I would like to thank everybody for the hints, some very detailed.
It all came down to one faulty ECC memory stick.
When I removed two modules (It seems that it only takes mem modules in
pairs) the machine runs just fine.
I tried to switch modules and run the ones I removed to rule out any
possibility of a system board failure, and
it was not able to start the Console firmware with those. So my
conclusion is that I have one faulty mem module.
Sad though since new modules cost a fortune. But I think I can live with
128 instead of 256MB RAM
since it will be used as a VPN router.