i am using the following nested query for update

where ESTIMATE2 is the table and its usedInPo field i want to update
for that i am using the nested query as select query it gives an error
when i am trying it to run from microsoftAccess

" Operation must use an updatable query ."

UPDATE ESTIMATE2 SET usedInPo = (usedInPo - (select quantity from purchaseitem where poid =132 and invoiceitemid = 3 ) ) + 6.0
WHERE companyid = 434 and estimateId = 77 and itemId = 3