subform references don't work that way; you have to drill down to the subform control, then reference the subform via .Form, and I don't think you can use Me either.
Try Forms("MainFormName").Controls("subformControlName ").Form where subformControlName is not the name of the subform, but its control.
This is one reason why it is good to not always settle for the names that Access form wizards create.
So it might be [Forms]![Main form name]![subform control name].[Form]![control name on subform].SetFocus, to set focus to a subform control, for example.
EDIT
to reference a control on a subform I use
[Forms]![Main form name]![subform control name].[Form]![control name on subform]
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.