I think I now verified the last assumption. I copied a file that has been created very early on the FS (in this case "menu.lst"), and moved it to "default", overwriting the problematic file. Then I recreated "menu.lst" using cp from "default", and sanitized "default" grub-set-default. Now the boot process works fine again.
I think I now verified the last assumption. I copied a file that has been created very early on the FS (in this case "menu.lst"), and moved it to "default", overwriting the problematic file. Then I recreated "menu.lst" using cp from "default", and sanitized "default" grub-set-default. Now the boot process works fine again.