The Bluecherry DVR is now in place at its site, where the DVR has two network interfaces: a private, wired network just the DVR and cameras, and a separate wifi connection to the Internet router.
I tried to add a third camera today. The prior two were added in my test environment, where only a single network interface was in use, and Internet connectivity was available on that interface. I don't know if that should make any difference.
When I clicked on Add IP Camera, it took nearly a full minute before it displayed the pull-down lists for camera type, etc. Everything except the first pull-down was disabled. My recollection from configuring the first two cameras is that selecting the camera brand (Brickcom) enabled the other form fields. Today it did not. The only way I was able to add the new camera was to go into the Chrome developer tools and delete the "disabled" attribute from the Camera Type pull-down. After that, I was able to continue the configuration of the camera.