error message saving new invoice

[address@hidden]

Hi all

I run gnue-forms to load invoices.gfd (from sample db in GNUe 0.7alpha1), then 
created a new invoice with just present customers and items.
When I save I receive the following message:

 ERROR:exception.admin.ConnectionError:Unhandled exception ConnectionError:
INSERT INTO invoice (customer, tax_total, grand_total, created, delivery, 
tax_rate, date, subtotal) VALUES (%(new_customer)s, %(new_tax_total)s, 
%(new_grand_total)s, %(new_created)s, %(new_delivery)s, %(new_tax_rate)s, 
%(new_date)s, %(new_subtotal)s)

  new_grand_total: 21.0
  new_created: datetime.date(2011, 4, 15)
  new_tax_total: 3.5
  new_customer: 3
  new_tax_rate: 20.0
  new_date: datetime.date(2011, 4, 15)
  new_subtotal: 17.5
  new_delivery: datetime.date(2011, 4, 20)

I don't understand it. What I did wrong?

Thanks,
Mat