Error when entering a sales order

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Hi List,

I haven't used LedgerSMB for entering sales orders before now, but I'm  
wanting to make a start.  However, when entering the first one, I get  
this error:

DBD::Pg::st execute failed: ERROR: duplicate key violates unique  
constraint "transactions_pkey"
Error!
INSERT INTO oe
(id, ordnumber, quonumber, transdate, vendor_id,
customer_id, reqdate, shippingpoint, shipvia,
notes, intnotes, curr, closed, department_id,
employee_id, language_code, ponumber, terms,
quotation)
VALUES
(10547, ?, ?, ?, ?,
?, ?, ?, ?,
?, ?, ?, ?, ?,
?, ?, ?, ?, ?)
ERROR: duplicate key violates unique constraint "transactions_pkey"

I've poked around the database, and I see that the highest value for  
transactions.id is 10545.  Furthermore:
select * from transactions where id = 10547;
 id | table_name
----+------------
(0 rows)

Any ideas as to what may be the problem?

Richard