Clear All Text Boxes On A Subform

I am using this code:

Code:
Dim ctlTextBox As Control
For Each ctlTextBox In Me.Controls
If TypeName(ctlTextBox) = "TextBox" Then
ctlTextBox.Value = ""
End If
Next ctlTextBox

to clear all text boxes on a Main Form.When I try the same code in the Form Load of the sub form - it says I can't assign a value to this object.I just want the Main Form and Sub Form textboxes to be empty when they both Load up.There is a selection combo box that will populate the main form and the sub form [Master-Detail] once a selection is made.Right now the main form has all empty textboxes but the subform datasheet is showing detail irrelevant records belonging to another master record and I want no data till a cmb box selection is made.