Solved. In case anyone runs into the same problem, you need to tell Windows to run "MF toolbox" when button is clicked. You then tell "MF toolbox" what to do when called that way: save in directory, email, etc.
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Hi,

I'm trying to configure a Canon Lasershot MF3110 scanner to save scan in folder when button is pressed which is possible according to manual.

Right clicking the corresponding icon in Scanners and Cameras folder of Control Panel allows indicating what Windows should do when button is pressed. It has four options: Run a particular program, ask user what to do, do nothing, and save in specified folder. Unfortunately the last option is disabled!

Anyone knows why?

TIA,

Alex