Alloc Magic is Broken

I did install clearlinux on a chromebook pixel 2 with changed MrChromebox firmware. I did not manage to get the sound running under Clearlinux and want to install another distro on the device now. When I am now entering the boot menu and try to boot another linux distro, I get the weird result:
Error: unknown filesystem
Alloc Magic is broken at 0x74ed9800: 74dFdFc0
Any idea how I could solve that issue?