I need to install OS X El Capitan 10.11 as guest OS in VirtualBox running on macOS High Sierra 10.13. I followed the instructions in this guide.
I obtained the OS X El Capitan image from here and modified it as outlined in the guide.
On startup I get a kernel/cpu panic and was unable to boot. What is going wrong here? I do not have a original copy of OS X El Capitan 10.11.
How do I resolve this situation?