The McAfee Web Gateway image can only be loaded on official McAfee WG appliances (and VMware).
You cannot install on any other server platform. Even if the hardware is identical to the hardware that McAfee supplies, it will not install.
Is this hardware purchased from McAfee?
If it is, you should contact McAfee support.
If it purchased from Dell or another vendor, it will not install.
Thank for your help, eelsasser.
I have installed my Web Gateway in a VMWare.
A couple of months ago I had tried on HT 6000 Pro desktop which installed successfully, but this time it didn't with the same ISO, the only difference is I might have changed are the hardrive and replaced RAM.
The installer checks if the hardware is running an official McAfee BIOS. This is somewhat simplified as there are a few special cases, but generally you can only install on hardware with McAfee BIOS or in VMWare virtual environment.
Changing Harddrive and/or RAM wouldn't have any effect on the installer, there must have been something different. Maybe a McAfee engineer helped you with installation the first time around?