I can't retrieve a scrollable ResultSet from CallableStatement

Hi,

I'm using posgresql 7.4 and I'm trying to receive a scrollable and updatable ResulSet with jdbc. But when I when I
checkthe type of the ResultSet I've retrieved its always FORWARD_ONLY. I use jdbc3 driver. 

the code:

       CallableStatement call = con.prepareCall("{ ? = call getRefcursor () }", ResultSet.TYPE_SCROLL_INSENSITIVE,
ResultSet.CONCUR_UPDATABLE);

        call.registerOutParameter(1, Types.OTHER);
        call.execute();
        ResultSet rs = (ResultSet) call.getObject(1);

        rs.last();   //this line throws the Exception

What do I need to do, to make it work!