Command not accepted...?

Hi All - looking for help diagnosing the following after the FlashOS step. Drivers all look good.:

Erase [=========================] 100% 2097152 bytes
Erase done.
Download [=========================] 100% 2097152 bytes
Download done.
File downloaded successfully
Transitioning to dfuMANIFEST state

C:\Windows\System32>meadow --MonoDisable
Opening port ‘COM8’
Unexpected error occurred: Command not accepted.

Got to the bottom of this, eventually. Culprit was a loop in App.exe that never gave up the thread control (via a Sleep). Even after flashing the OS the old App.exe survived and once it started the device would not accept any commands thereafter.