You may need to either cast your control reference to a more specific class, or select a different class on the property node.
I create a gauge and created a property node that was scale.maximum. So I knew it existed. Then I disconnected the property node from the control, then the top of the property node function said Knob(strict). Then I right clicked on it and drilled down through the classes until I found the bottom level. The screen shot is attached.
I bet that a simple generic wouldn't have a scale so the property node does not exist, that it is a property of the more specific control.