Most of us here don't use macros, favoring code instead. Your issue is probably how you're referencing the control in question. Using the builder will pretty much get it right all the time, or you can try to figure out how to apply the syntax to reference subform controls:
Forms!YourFormName.yourSubformControlName.Form.NameOfControlHere
SubformControlName is the name of the control that contains the subform. It might be the same name as your subform (if you used a wizard) but I do not allow that.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.