ClassCastException org.postgresql.jdbc3.Jdbc3Connection

I am trying to get the PGConnection/Jdbc3Connection object from
Connection class.
The connection class returned is
org.jboss.resource.adapter.jdbc.WrappedConnection (as I am using JNDI in
JBoss).

When I try to get the underlying connection and cast it to
Jdbc3Connection I am getting a class cast exception.

Below is the code.
Connection conn =
((WrappedConnection)DBConnection.getConnection()).getUnderlyingConnection();
LargeObjectManager lobj =
((org.postgresql.jdbc3.Jdbc3Connection)conn).getLargeObjectAPI();

In the above code DBConnection class provides a method to get the
connection object from the pool.

Exception:
09:42:33,016 WARN [RequestProcessor] Unhandled Exception thrown: class
java.lang.ClassCastException
09:42:33,017 ERROR [[action]] Servlet.service() for servlet action threw
exception
java.lang.ClassCastException: org.postgresql.jdbc3.Jdbc3Connection

As you can see it says that the object is of type Jdbc3Connection so why
does it give a class cast exception then?

I am using postgresql-8.1-404.jdbc3.jar driver & the database is 8.1.3.

Thanks,
-Prasanth.