So I built a new USB key (fob\dongle) with ESXi 5.5 to put into my home lab white box. Ok sweet, configured the management network all good. Re-registered all my VMs, set some auto start ups.
Shutdown server, come back next day, start the server up. None of the VMs are registered.

Hmmm. I am positive I didn’t skip any steps. How hard is it? I have done this many times before. Oh well maybe I was on auto pilot did something silly. Not sure what, but hey whatever. Registered the VMs again.
Next day same thing. Now I know I did it correct, how can I not. Make the changes again, restart and all the changes are gone. What the? Change the IP address of the ESX for something different. Each time I reboot goes back to the original IP address I set up and all the VMs are no longer registered.

Did some research. (Read google) and found a blog post on the VMware communities (ESX 5.1 config changes do not save) where someone had two identical servers however one had the USB key in a USB 3.0 port and the other the USB 2.0. Not sure why you would have the USB key in different ports if the hardware itself is identical. Anyways that turned a light bulb on for me. Checked what port my USB was in, USB 3.0. So moved it to a USB 2.0 port.

That did the trick. Was able to make changes, restart and all the changes now stick. Not sure what and no one answered the VMware communities post but there you have it.

All I can think of is that I initially had the USB key in a front USB 2.0 port for the initial configuration. Then transferred it to a USB 3.0 port at the back of the server once I was happy with it.