Do you have other devices show up in the FSX control setting such as virtual joystick, mouse and CH yoke? If you have more than one device such as virtual joystick/mouse and CH yoke that assign to the same function control, Prop control for example, this will cause a conflict between them and might disable the prop control function in CH yoke. Just disable or uncheck the other devices that assign to the prop control except the CH yoke.
This is my wild guess.