In this tutorial, you will learn how to fix this kernel requires an x86-64 CPU but only detects an i686 CPU
when booting Android ISO on Virtualbox. If you are trying to boot android ISO on virtualbox and you get this error, it basically means the cpu type that this virtual machine is using is not supported.
This error can be fixed easily by setting the correct CPU type when booting up Android x86 ISO on virtualbox.
Launch Virtualbox
Launch Virtualbox, and go to the machine that you created for Android ISO, next you need to right click over the machine name, and go to Settings, as shown in the image below.

Set correct CPU Architecture
Next, once settings window opens, you need to go on General settings which is located at the top left of the sidebar

Now you need to set Type to "Linux" and Version to "Other Linux (64-bit)" and save the settings by clicking the OK button.
Start VM
Onc you set the correct CPU type, start the vm and the error should be gone. If the error continues even after changing the cpu type settings, try to recreate the virtual machine using this setting for cpu.

Conclusion
In this tutorial, we explained step by step how to fix the error "this kernel requires an x86-64 CPU but only detects an i686 CPU" which happens when the cpu type is not supported by Android or when like in our case the wrong type of CPU was being used on Virtualbox as CPU when booting Android x86.