ERROR: The backend has broken the connection -- AND: FATAL: Socket command type unknown

Hi,

I have some problems with jdbc and postgresql 7.3.
I've developed a class java to read form file, to get interesting
information and to store them in database. The class gets connect with
postgrsql by jdbc (pg73jdbc3.jar) without problems. It does some
queries (select, update, insert) but a error happens in the same point.
The error message in the java class is:

ErrorCod: 0
Message: The backend has broken the connection. Possibly the action you
have attempted has caused it to close.
State: null

The query inserts data in the database and gets identificator by
function.
I execute the query by psql and there isn't any problem. I check if the
query has been executed in postgresql by java class, and yes, it has
been executed correctly. But the data isn't got by java class.

There is a error message in postgresql:

FATAL: Socket command type unknown

I don't know what is happened. I've changed the query but the errors go
on. The query is executed in a method of the class and the error
appear after 5 queries are executed correctly in the same method.

I need help because I don't know where is the problem.

Thanks in advanced.

Toni.