Hi this is working:
=IIf(Forms!GARF!GARFsubForm![finished_good_#]<>"", DLookUp("[CustomerSKU]","ItemCustomerSKU", "ItemNumber = '" & Forms!GARF!GARFsubForm![finished_good_#] & "' AND Customer = '" & Forms!GARF![customer] & "' AND Company = '" & Forms!GARF![company] & "' AND MarketingSeason = '"...