It was just me, not paying attention to details. Here's what I intended:
SELECT dbo_Stock.stk_item_no, dbo_SalesItems.s_descript, dbo_Stock.stk_inv_qttytd, dbo_Stock.stk_row, dbo_Stock.stk_aisle, dbo_Stock.stk_bin, IIf(IsDate([stk_bin]),CDate([stk_bin]),"") AS bin
FROM dbo_SalesItems INNER JOIN...