[SOLVED] Does GC1.20 work with Firmware 1.23 ? (no Motor Movement)

I’ve got everything built, firmware 1.23 loaded from github, and GC 1.2 installed from the Windows installer.
Just trying to do the “Test Motors/Encoders” but am not getting any movement yet.
It times out saying:

“It is possible that the serial port selected is not the one used by the Maslow’s Arduino or that the firmware is not loaded on the Arduino.
Connected on port COM3
PCB v1.2 Detected
Grbl v1.00
Ground Control 1.20
Firmware Version 1.23”

I would assume that the firmware is successfully loaded since it actually reports it’s version.
GC reports “Connected” above the serial window.
I verified the Port assignment (Com3) to the Arduino.
I tested the cables (pinouts, continuity, & isolation).
I bench tested the Power Supply.
Thanks to the warnings of others, I was paranoid about plugging the shield PS into the Arduino by mistake and am sure I’ve never done that.

Maybe the warning that I get about GC v1.20 being too old is correct?
Is there a mismatch between GCv1.20 and Firmware v1.23 ?

Other Ideas?

Quite embarrasing - I did not think (until now) to try re-starting GC after everthing was connected.
It works fine after restarting GC.