Andy,
thanks for the suggestions.
I had tried the GParted image before. In fact, using their image first
brought up the boot error in my case and the GParted developers pointed
me to debian, as this is their underlying system.
I have now also tried to boot with "secure boot option" enabled, but the
outcome is the same.
So, unfortunately, no luck with these.
Since - as I stated in the original post - a similar problem occured in
the openSUSE installation medium (and could be resolved there), I guess
it is quite obvious that it has to do with the combination of firmware
and the non-modified boot code.
Best regards
Bernd
