Original Codec version is 1.6.7(4212) downgraded from 1.8.0(55)P1 after registering CM.
From GUI system status show:
Video cable: OK Power cable: Standby; Display Diagnostics: Error
What you describe usually means that the HDMI cable is connected to the wrong HDMI port on the display.
HDMI cable needs to be plugged into the primary HDMI port with the white display icon (further from the center) instead of the aux port with the orange display icon. Can you have this verified?
If I am right on the following assumptions:
Then, could you provide the output of command "show upgrade detail" while in display is active i.e. while in a call?
In CTS 1.6.X code, we cannot read the serial number of the GEN4 displays, which may be why you're receiving the error. In CTS 1.7.1 and higher we are able to read the serial number of the GEN4's. Did you see the same error when the unit was at 1.8.0, prior to downgrading to 1.6.7?
On the WebGUI, do you see the display serial number listed (Display_Serial, should be in the same area as the Display_Hardware model/Display version you posted a screenshot of earlier)?
In addition to Antonio's suggested output of "show upgrade detail," you should see the serial number listed in the output of "show hardware video."