So the mystery deepens. I replaced the nVidia card with an ATI Radeon 5450 card, the same that is in the 1`5.5 machine The problem persists with Workstation 17.5. So right now it appears to be something with Workstation 17.5 or something else with this particular machine.
To isolate this once and for all, I have a third Sandbox test machine which has the same nVidia GeForce 710 card in it and the same hardware. I will install 15.5 on it, see if both the 9.2.6 and 11.0.6 OVAs work. If so, then I will do the in place Workstation upgrade to 17.5 and see what happens.
I'll keep folks posted.
Jeff