We've seen something kind of similar to this, where a listbox is inaccessable on a page when the refresh is called on another, non-active page which contains a listbox in the same position.

If this is the problem, you can work around it by not calling the refresh of the non-active page.
>>You mentioned that in your app the listbox appears on a page.
>>
>>By any chance, is the refresh of another page being called from the Activate, or some other method, on the page with the inaccessible list box?
>>
>A little bit more info:
>
>The form has a combobox and 4 listboxes one under another visually. The visible property of listboxes is not changed in run-time. The listboxes have code in LostFocus and InteractiveChange. Originally all listboxes appear blank (empty) and only after you select items, the next listbox (which is right under) gets populated. We're unable to select the last (fourth) listbox in VFP9.
>
>Here is the code from InteractiveChange event of the ListBox.
>

>LOCAL luRetVal
>
>luRetVal = DODEFAULT()
>thisform.refreshpagedata(this.name)
>RETURN luRetVal

>
>And the RefreshPageData has some heavy code using thisform.pgfOthers.page1.&lcObjName.