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?

>>3 listboxes one under another.
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>>What do you mean by "one under another"? Do you mean that you only see one list box at a time and determine via code which list box should be visible, manipulating its visible property and calling its zOrder method?
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>>If this is what you mean, I encountered something similar just yesterday. If this is not what you mean, I have never seen this problem. My problems went away as soon as I made all the list boxes visible.
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>No, I meant, that on form we have combobox, then beneath it is one listbox, then another beneath this and finally one more at the bottom of the form. They all are visible. That's my colleague's form, I believe, he populates these listboxes in run-time and adds them programmatically in code. I think there was another thread about this problem quite recently.
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>Also here is how form works: then the form appears, all the listboxes are empty. You select an item in the top combobox, then the first (top) listbox shows data, you select some items, then the second listbox shows data and finally the last. In VFP9 we're unable to select anything in the bottom listbox. It works fine in VFP8.