SQL Problem - Trying to update a table with data from another tab le

["Batchelor, Mildred @ HFS" <MBATCHELOR@CKR.COM>]

I am trying to update a table with data that I have created in another table
with no success.  I am getting an error message that table has not been
selected (the table that I am trying to pull from).  Here is the script.
Can someone please tell me what I am doing wrong?

Update PS_BU_ITEMS_INV

  set  PS_BU_ITEMS_INV .QTY_RESERVED =  (SELECT
c_ps_sum1_demandin.qty_allocated
                                                                        FROM
c_ps_sum1_demandin B

              WHERE PS_BU_ITEMS_INV.BUSINESS_UNIT = B.BUSINESS_UNIT
                    and  PS_BU_ITEMS_INV.INV_ITEM_ID = B.INV_ITEM_ID);

Thanks
Mildred Batchelor
mbatchelor@ckr.com