I tried to install Debian by mounting the ISO as virtual CD-ROM using IPMI.
In the BIOS I choose the "UEFI: IPMI Virtual CD-ROM" device for boot.
The image was detected and GRUB was booting, but the following error message appeared:
The boot process continued and the Debian install menu was shown (but with slightly different font layout of the text, but still...).Error prefix not set
When I selected "Install", the screen went blank and that was it. Nothing happened.
[SOLUTION]
Thanks to a post on ubuntuforums about this error message, it pointed into direction of "UEFI" causing problems.
So I went back to the BIOS and selected the "IPMI virtual disk", which did not have the "UEFI:" prefix.
Now the Debian installer booted and worked as expected.