The code works. You probably don't have the tag property quite right. Suppose your SQL statement did contain the Where clause, would it look something like this?
SELECT
tblSales_Item_data.Location_Num,
tblSales_Item_data.Opr_Del_Dt,
tblSales_Item_data.Product_Item_ID,
tblSales_Item_data.Item_Cd_Desc,
tblSales_Item_data.Item_ID,
tblSales_Item_data.Attr1,
tblSales_Item_data.Attr2,
tblSales_Item_data.Attr3
FROM tblSales_Item_data
Where tblSales_Item_data.Location_Num In (2,3);
If so, then the Tag Property for the list box should look like this (Assuming the Location_Num is defined as a Long Integer)
Where=tblSales_Item_data.Location_Num,Long;
or it could, optionally, look like this:
Where=tblSales_Item_data.Location_Num,Long,=;
Also, make sure your syntax for the docmd.openreport is correct:
Docmd.OpenReport "rptName",acViewPreview",,BuildWhere(Me)
To test it, instead of issuing the DoCmd.OpenReport, issue this command instead:
MsgBox BuildWhere(Me)