The mouse events were trying to be used in the 'View Controller' class.
I've since found a sample code (3rd party) that shows they have to be in the 'NSView' object, so I've had to create a custom NSView object programatically to track the mouse and it's all working.
Here's the URL:
http://www.markdouma.com/developer/MouseMovedvsTrackingAreas.zip