problem with Serialize.store

I've a problem with Serialize.store.

I get this message:

Exception in thread "main" java.sql.SQLException: ERROR:  Attribute
'miaclasse' not found

    at org.postgresql.core.QueryExecutor.execute(QueryExecutor.java:103)
    at org.postgresql.Connection.ExecSQL(Connection.java:398)
    at org.postgresql.Connection.ExecSQL(Connection.java:381)
    at org.postgresql.util.Serialize.storeObject(Serialize.java:392)
    at org.postgresql.util.Serialize.store(Serialize.java:278)
    at Connessione.main(Connessione.java:18)

for the attached piece of code (3 class). I don't get this message If I
declare attribute "m" of class prova "private" or "protected".

Someone can help me?
THANK'S!!!!


************************************************
Connessione.java (main class)
************************************************
import java.io.*;
import java.sql.*;
import org.postgresql.util.*;
import org.postgresql.core.QueryExecutor;

public class Connessione
{

 public static void main(String args[]) throws Exception
 {
     org.postgresql.Connection conn;
     prova m = new prova();
     prova obj;
     Class.forName("org.postgresql.Driver");
     conn =
(org.postgresql.Connection)DriverManager.getConnection("jdbc:postgresql:provaASI",
"daniele","");     // works
     org.postgresql.util.Serialize.create(conn, m);     // makes   problems
     org.postgresql.util.Serialize s = new Serialize(conn,m);
     int oid  = s.store(m);
     obj = (prova)s.fetch(oid);
     System.out.println(obj.number);
 }
}
************************************************
End Connessione.java
************************************************

************************************************
prova.java
************************************************
import java.io.*;
import java.sql.SQLException;

public class prova implements  Serializable {

    public int number;
    public miaclasse m;

    public prova()   throws ClassNotFoundException,
FileNotFoundException,IOException, SQLException
    {
      number=4;
      m = new miaclasse();
    }
}
************************************************
End prova.java
************************************************

************************************************
miaclasse.java
************************************************
import java.io.*;
import java.sql.SQLException;

public class miaclasse implements Serializable {

    String s;
    public int i;

    public miaclasse() throws ClassNotFoundException,
FileNotFoundException,IOException, SQLException {
        i=323;
        s="stringa";
    }

    public String getS() {return s;}
}
************************************************
End miaclasse.java
************************************************