Thanks Santhosh,
I had already tried this, but I've found an answer now.
For some reason the set-up defaults to the Omnipage SE application to scanner handle events.
Try this:
Power on the connected printer and place a document to scan on the platen.
Press the SCAN button on the printer.
At the bottom of your desktop window stack a window pops up inviting you to choose Omnipage or or MP Navigator applications to handle the scan.
Select the MP Navigator option and continue. MP navigator will continue to work until you power down the printer and re-start it.
Scanning from the printer driver (Control Panel\Hardware and Sound\Devices and Printers\Canon MP140 series Printer) works all the time, but you loose the MP Navigator functionality.
I'm sure that here is a better way to fix this, but the above works fine for me for now.
Mike