Duilio,

> the script inserts a new record in table A.
>
> A constraint states that the containt of FIELD1 must be in table B.
>
> I was editing exactly the record in table B the referenced the containt of
> FIELD1 of the record to be inserted.

That should have not created a deadlock at all, reads never block writes.
What transaction isolation were you using on your insert statement?