problem in getting Large Object from pooled PostgreSQL / Tomcat 6

hello

I am trying to Retrieve image ( Large Object) from pooled PostgreSQL /
tomcat 6:

I am having some exceptions from following

ds = (DataSource) ctx.lookup("java:comp/env/jdbc/bzk2");
Connection conn = ds.getConnection();
PGConnection pgCon = (PGConnection) ((DelegatingConnection)conn) //
****exception
.getInnermostDelegate();

lobj = ((org.postgresql.PGConnection)pgCon).getLargeObjectAPI();

SEVERE: JSF1054: (Phase ID: RENDER_RESPONSE 6, View ID: /iki.jsp)
Exception thrown during phase execution:
javax(dot)faces(dot)event(dot)PhaseEventsource=com(dot)sun(dot)faces(dot)lifecycle(dot)LifecycleImpl(at)1f0f0c8
Dec 19, 2008 6:04:21 PM org.ajax4jsf.webapp.BaseXMLFilter doXmlFilter
SEVERE: Exception in the filter chain
javax.servlet.ServletException:
org.apache.tomcat.dbcp.dbcp.PoolingDataSource
$PoolGuardConnectionWrapper cannot be cast to
org.apache.commons.dbcp.DelegatingConnection

how can I solve the problem ?

regards