Save java objects using JDBC

I'm sorry to bother the list with this question - I know people are
always asking it.  I thought I understood how to do this, but my code
doesn't work.

I am trying to save a java object in a database using the setBytes()
method of PreparedStatement - I don't want to use the large object manager
because I want this to be somewhat portable.

The code below gives me the error: 
Exception: FastPath protocol error: Z :: FastPath protocol error: Z
As soon as I call setBytes()

I thought this only came when you forget to call "setAutoCommit(false)".
Can anyone please tell me what I'm doing wrong. 

Thanks a lot, Rob


-------------------- PSQLTest.java -----------------------

import java.sql.* ; 
import java.io.* ; 
import java.util.* ;

public class PSQLTest {      public PSQLTest() { }      public static void main(String[] args) {
Vector vec = new Vector() ;for (int i=0; i<10; ++i)     vec.addElement(new Integer(i+5)) ;
Connection conn = null ;try {    Class.forName("postgresql.Driver") ;    conn = DriverManager.getConnection
("jdbc:postgresql://127.0.0.1:5432/rob","rob", "") ;    conn.setAutoCommit(false);
 
    byte[] bytes ;    ByteArrayOutputStream out = new ByteArrayOutputStream() ;    ObjectOutputStream objOut = new
ObjectOutputStream(out);    objOut.writeObject(vec) ;    objOut.flush() ;    bytes = out.toByteArray() ;
objOut.close();
 
    PreparedStatement ps = conn.prepareStatement     ("insert into vectors (name, id) values ( ?, ?)") ; 
    ps.setString(1, "Vector name") ;    ps.setBytes(2, bytes) ;     ps.executeUpdate() ;     ps.close() ; 
    conn.commit() ;} catch (Exception e) {     System.out.println("Exception: "+e+" :: "+e.getMessage());
e.printStackTrace();}
 

   }   
}