Access 2010 Web db: syntax for referring to forms/subforms

After mastering and using subform navigation for years in the Access client, along comes the web database and a similar, but not identical, way of referring to subforms.

I have a main form named "Navigation Form" with 4 tabs: MS Management, MS Management (Table View), Summary Management, and Search Form. The first three tabs each display an ordinary form. The Search Form on the fourth tab contains a Combo Box and a subform named Search Subform.

I am trying to figure out exactly how to refer to a control "ParentID" on the Search Subform in a macro that runs on the AfterUpdate of the Combo Box on Search Subform's parent, Search Form.  I have tried every permutation of forms I can think of, based on examples from all over the web, and they all return the error "..does not contain the Automation Object..." or "...must use a valid Path...".

I understand the meaning of these errors, but so far I have not stumbled onto the correct Path specification. Can anybody set me straight using the form names I included above?