If you got an ESXi hosts running and you want to run an ESXi server as in virtual machine and add VM's to the virtualized ESXi host, these nested VM's won't start. Error message:

ESX Running VMware ESX in a virtual machine requires the outer virtual machine to be configured for running a VMware ESX guest operating system. You cannot power on a virtual machine until the outer virtual machine is reconfigured.

The solution is simple, not supported by VMware:

    * Shut down the virtual ESXi5 VM
    * Click Edit Settings (of that VM)
    * Click the Options tab
    * Click Advanced / General / Configuration Parameters…
    * Click Add Row
    * For the Name/Value enter: monitor_control.restrict_backdoor / TRUE