Every year, for the International User Conference, Esri's IST staff prepare an image for hundreds of computers in the Showcase. Why I've never encountered this issue before, I have no idea, but this year I was seeing the following error in the ArcGIS Server Manager web application when attempting to 'Create Site':
Failed to create the site. Failed to configure the server machine 'WHATEVER-NAME.ESRI.COM'. Server machine 'WHATEVER-NAME.ESRI.COM' is not a local server machine.
It turns our that there is an XML file, which the ArcGIS Server Manager creates, which contains information on the machine. The machine image, of course, picks up this file, and when the machine to which the image is applied is assigned a different name, ArcGIS Server site creation fails.
The solution is to either edit the XML file to update the machine name to match the localhost's current name ... or stop the ArcGIS Server service, delete (or simply rename) the XML file, then restart ArcGIS Server and launch the Server Manager web application (which should recreate the XML file with the correct machine name). Here's the file path and name: