Enterprise JavaBeans :: Calling Singleton Bean From Session Bean Returns NullPointerException

I am doing this

@Startup
@Singleton
@ConcurrencyManagement(ConcurrencyManagementType.CONTAINER)
@Lock(LockType.READ)
public class ResourceBean {

[Code] ....

And I call this singleton bean from a stateless session bean like this

@Stateless
public class ClientBean {
@EJB
ResourceBean resource;

public String create(String r)
{
String res=resource.returnString(r);
return res;
}
}

But resource.returnString(r); gives a org.apache.jasper.JasperException: java.lang.NullPointerException I started the glassfish server in debug mode and found out that "resource" was null. but @PostConstruct in singleton does print which means singleton bean exists.

Can we call singleton beans with no interface in such a way form a session bean? I actually want to acquire instance of singleton bean when a client invokes method in Client bean...