Referencing subform controls always throws Access users for a loop while they're new to using Visual Basic for Applications (VBA). That's because Access views the subform as just another one of the form's controls.
To refer to a form, identify the form via the Forms collection as follows:
Reference specific controls and subforms via the form's Controls collection:
The subform is actually a control, but it's a control with dependent controls. That means you must identify both levels: the subform and the subform's controls. To do so, use the subform (control's) Form property in the form:
If the object name contains spaces, you must enclose any instance in brackets:
Forms![form name]![control name].Form.[control name]
In addition, you can use the Me identifier when the form is current, as follows:
Susan Sales Harkins is an IT consultant, specializing in desktop solutions. Previously, she was editor in chief for The Cobb Group, the world's largest publisher of technical journals.