JNDI Datasource in tomcat

Hi

Im trying to get a connection through a JNDI service in tomcat. Im
trying wuth this config.

<Resource
    auth="Container"
          name="jdbc/openbravo"
          type="org.postgresql.jdbc3.Jdbc3SimpleDataSource"
          driverClassName="org.postgresql.Driver"
          password="postgres"
          maxIdle="5"
          maxWait="10000"
          user="postgres"
         maxActive="20"
    databaseName="openbravo"
    serverName="127.0.0.1"
    portNumber="5432"
    factory="org.postgresql.jdbc3.Jdbc3ObjectFactory"/>

using thi driver. pg74.216.jdbc3.jar
I get this error
- org.postgresql.util.PSQLException: A result was returned when none was
expected.
- Unable to create a connection pool
org.openbravo.exception.PoolNotFoundException: Failed when creating
database connections pool: org.postgresql.util.PSQLException: A result
was returned when none was expected.

Here
 Context initctx = new InitialContext();
 Context ctx = (Context) initctx.lookup("java:/comp/env");
 DataSource ds = (DataSource) ctx.lookup(jndiResourceName);
con = ds.getConnection();
-- Here i get a org.postgresql.jdbc3.connectionjdbc3
 PreparedStatement pstmt = con.prepareStatement(dbSessionConfig);
pstmt.executeUpdate();  <--- Here a got the error

when i used the driver manager with this driver jdbc3-postgresql.jar i
think that i got another kind of connection and i havent got no error.
seems that now i have a config error but i dont really know whats the
correct way to fix it

can someone help me

Thanks and regards