Why has my query suddenly gone read only

>I am using access 2003. I have a form which is based on a simple
query. Previously I could edit the data on the form, but now it is
read only. The form has not changed and neither has the query. The
query is based on two tables, POs and PO-Items, and the SQL is as
follows:
>
SELECT [PO-Items].OrderID, POs.Stock, [PO-Items].ItemID, [PO-
Items].Part, [PO-Items].Unit, [PO-Items].Desc, [PO-Items].Qty, [PO-
Items].QtyDelivered, [PO-Items].Price, [PO-Items].DateRequired, [PO-
Items].EnteredItem, [PO-Items].DEPT_NAME, POs.[job#], POs.ACCOUNT_REF,
POs.Client, POs.desc, POs.delivery, POs.RequestedBy, POs.Stock,
POs.contact_name, POs.[Call_Off/Notes], POs.EMPLOYEE_ID,
POs.order_date, POs.PO_Complete
FROM [PO-Items] INNER JOIN POs ON [PO-Items].OrderID = POs.OrderID
ORDER BY [PO-Items].OrderID;
>
POs.OrderID is an autonumber field. PO-Items also has an autonumber
field, but it is not used in this query.
>
About 3 days ago, there was a data corruption on the POs table, and
one of the rows just had #ERROR in every field. I compacted the
database and everything seemed ok, but one row of data was missing. It
is since this compact that the query has been read-only. The problem
seems to be with the POs table, because if I import an old copy from
before the data corruption, the query becomes editable again.
>
Can anybody suggest why this might have happened, and how I might be
able to fix the problem?
>
Thanks for any help
>
Colin
>

Open the table in design view, and see if there is a primary key.
>
Sometimes after a crash/corruption, a unique index goes bad. When you repair
the database,Accessremoves the index (rather than remove the data that
violates the index.) You might have a table named "MSysCompactErrors" or
similar, indicating that this happened.
>
In any case, the lack of a primary key/unique index on the fields that join
the tables in a query can make itread-only.