Returning Values From Table to ListBox

[EMoore12]

I have a form that has a combo box that contains items and a multi-select list box that contains values. The multi-select list box is populated based on the item that is selected in the combo box. What I want to happen is once the user selects an item from the combo box, if that item already exists in the table then the values that exist for that item should appear in the multi-select list box. Here is a snippet of the code I have on the after update of the item field.

lstItemValue.RowSource = DLookup("ItemValue", "tblExclusion", "[State]=forms!frmExclusion!txtState" & _
" And [Event]=forms!frmExclusion!txtEvent" & _
" And [Year]=forms!frmExclusion!txtYear" & _
" And [Revisingcode] = '" & strRevisingCode & "'" & _
" And [ItemName]= '" & strItemName & "'")

This code prompts me with a parameter box.

Any help would be greatly appreciated.