Probably you have " =ADir(fai_array ... " somewhere in the form events. Then fax_array became a LOCAL variable and the listbox cannot get it.

Try this:

thisform.addproperty("fai_array[1]",.f.)
=ADir(thisform.fai_array,......
ThisForm.List1.RowSource = "thisform.fai_array"

>When I run this on my form I get an empty list box even though there are two items:
>
>=ADir(fai_array,(pdm_var.this_release_directory) + Left(pdm_var.fai_part_number,6) + "*.pdf")
>ThisForm.List1.Visible = .T.
>ThisForm.List1.RowSource = "fai_array"