Android x86 in VirtualBox: “FATAL: NO BOOTABLE MEDIUM FOUND. SYSTEM HALTED” directly after installation “FATAL: NO BOOTABLE MEDIUM FOUND. SYSTEM HALTED” appears on Android x86 6.0 rc3, but not on Linux Mint or Windows XP, immediately after installation.

The boot order is correct.What might be wrong?
That was likely a flaw in Android x86 Marshmallow, which has already been patched in Android x86 Nougat, according to my tests.