Java Proxy Client Error

I write a EJB client to call the deployed java proxy, but I got the following exception, sounds like

authorization error, but I have already used the xiappluser to access.

Exception in thread "main" com.sap.aii.proxy.xiruntime.core.BaseProxyException:

Error sending MS message. Exception: Received HTTP response code 401.

at com.sap.aii.proxy.xiruntime.core.AbstractProxy.send$(AbstractProxy.ja

va:146)

.....

Here is the my code:

Properties p = new Properties();

p.put(Context.INITIAL_CONTEXT_FACTORY,

"com.sap.engine.services.jndi.InitialContextFactoryImpl");

p.put(Context.PROVIDER_URL, "<sid>:50104");

p.put(Context.SECURITY_PRINCIPAL, "xiappluser");

p.put(Context.SECURITY_CREDENTIALS, "****");

Context ctx = new InitialContext(p);

....