Back door solution seemed to work.
Copied BIM server from my old machine. As expected, that didn't work. BUT it meant there was a copy of BIM server on the machine, so my install disk was happy to repair it. And now everything runs fine. Why the install disk wouldn't just delete whatever phantom files existed before the copy, I don't know.
Just happy to have it all up and running. Tomorrow I give back my old machine and fly free on my own!