Fred - you are THE MAN!! I've been stuck on this for the past two days and would never have figured it out. Who would've guessed that the USB stick creator was to blame since it worked on my other systems.
So far it's mixed success. I created two USB keys - the 32GB one with ESXi 5.5 and the 4GB with ESXi 5.1.
On every server, the install for 5.5 gets stuck on "loading lsi_mr3.v00" and won't continue past that point. The install for 5.1 just completed for another server and will try loading it on the next one.
Optimally I'd like to get 5.5 installed to play with the latest and greatest. Maybe it's a limitation of the servers themselves not being supported on HCL?
Thank you again for your help.