Populate Subform from ListBox

[kappa]

Hi All,
I am relatively new to Access and trying to construct a simple Stock Inventory Databse.
I have two main tables for stock - TblPlu, which holds all the child items (product items ie. Pint Guinness etc..) TblMasterStock - which holds all the
parent items (keg guinness etc.. ).
End Result trying to reach: - On the MainStock form the user can enter Master Stock Item No, Decsription etc.. , then save record. The user can link a plu item by double clicking on an list box selection. A subform is attached to this MainStock form to show all linked plu items to the master stock item..
The problem area is getting the list box selection to write the MasterStockItem No back into TblPlu Table, where the subform can be filled via the query..

Where I am getting stuck is trying to write a value back into the MasterStockItem field of Tblplu_in....

What I have is...
On the dbl click event of listbox

StockItemNo.Value = Str$(PluFindings.Value)
Tblplu_in.MasterStockItem = Form_FrmMasterStock.Stock_Item_No.Value

I am getting an 'Object Required' when trying to run this...


The query for subform is
SELECT Tblplu_in.Plu_no, Tblplu_in.Plu_Name, Tblplu_in.Dept_No, Tblplu_in.Stock_Link, Tblplu_in.MasterStockItem, Tblplu_in.Plu_Size_No
FROM Tblplu_in
WHERE (((Tblplu_in.MasterStockItem) Like [Forms]![FrmMasterStock]![Stock_Item_No]));

Thanks..