So you have a total of 3 forms here? Form 1 (parent) with Form 2 (child) and then a third form that is being updated? You want closing Form 3 to trigger a refresh of a listbox on Form 2? Is that right? If so, in the OnClose event for Form 3, just say:

Forms!Form1!Form2.Form!ListBox.Requery

That should do the trick - if I'm understanding your question correctly. I've had something like this before where a subform had a listbox (let's say products) and you want to add a new product in a popup form, and when that form closes, requery the list of products.