Can a Deployable Proxy be called from Login Module?

Is it possible to call a deployed proxy from a customized login module. We have created both but have been unable call it fromt the logon module. We have tried this code:

javax.naming.Context context = new javax.naming.InitialContext();

com.sap.a3.proxy.A3Service service = (com.sap.a3.proxy.A3Service) context.lookup("java:comp/env/A3ServiceProxy");

But receive the error:

NamingException: com.sap.engine.services.jndi.persistent.exceptions.NameNotFoundException: Object not found in lookup of A3ServiceProxy.

Any help would be much appreciated...