When you're trying to run 64-bit hosts inside a virtualized ESXi host you may get the following error. The virtual machine requires hardware features that are unsupported or disabled on the target host: * Longmode: required for 64-bit guest OS support. On Intel systems, longmode requires VT-x to be enabled in the BIOS. On nested virtual ESX hosts, longmode support normally requires upgrading your VM to ESX 5.1 compatibility level (VM version 9) and enabling the "Virtualized Hardware Virtualization" flag on the outer VM. For incompatibilities other than NX/XD or longmode: if possible, use a cluster with Enhanced vMotion Compatibility (EVC) enabled; see KB article 1003212. Even though the processor mode is set to Intel VT-x or AMD-V This is quite simple to fix, you just need to enable nested virtual machines by adding the following line to your ESXi virtual machines .vmx file vhv.enable = "TRUE" More information can be found in this arti...