I am starting JBoss with the simplest code （an interface and its implementation as Session Bean), which was packed in an JAR file and copied to ..\server\default\deploy folder. However, I got the exceptions when started the JBoss server (jboss-4.2.3.GA). Any idea what could cause such exception? Thanks in advance.

21:33:12,203 WARN  [ServiceController] Problem starting service jboss.j2ee:jar=HelloWorld.jar,name=HelloWorldBean,service=EJB3
java.lang.IllegalArgumentException: com.hongliang.ejb3.impl.HelloWorldBean is not an interface
    at java.lang.reflect.Proxy.getProxyClass(Unknown Source)
    at org.jboss.ejb3.stateless.BaseStatelessProxyFactory.init(BaseStatelessProxyFactory.java:166)
    at org.jboss.ejb3.stateless.StatelessRemoteProxyFactory.init(StatelessRemoteProxyFactory.java:113)
    at org.jboss.ejb3.stateless.BaseStatelessProxyFactory.start(BaseStatelessProxyFactory.java:212)
    at org.jboss.ejb3.stateless.StatelessRemoteProxyFactory.start(StatelessRemoteProxyFactory.java:120)
    at org.jboss.ejb3.ProxyDeployer.start(ProxyDeployer.java:83)
    at org.jboss.ejb3.SessionContainer.start(SessionContainer.java:157)
    at org.jboss.ejb3.stateless.StatelessContainer.start(StatelessContainer.java:102)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.ejb3.ServiceDelegateWrapper.startService(ServiceDelegateWrapper.java:103)
    at org.jboss.system.ServiceMBeanSupport.jbossInternalStart(ServiceMBeanSupport.java:289)
    at org.jboss.system.ServiceMBeanSupport.jbossInternalLifecycle(ServiceMBeanSupport.java:245)
    at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:155)
    at org.jboss.mx.server.Invocation.dispatch(Invocation.java:94)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:86)
    at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
    at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:659)
    at org.jboss.system.ServiceController$ServiceProxy.invoke(ServiceController.java:978)
    at $Proxy0.start(Unknown Source)
    at org.jboss.system.ServiceController.start(ServiceController.java:417)
    at sun.reflect.GeneratedMethodAccessor9.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:155)
    at org.jboss.mx.server.Invocation.dispatch(Invocation.java:94)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:86)
    at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
    at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:659)
    at org.jboss.mx.util.MBeanProxyExt.invoke(MBeanProxyExt.java:210)
    at $Proxy57.start(Unknown Source)
    at org.jboss.ejb3.JmxKernelAbstraction.install(JmxKernelAbstraction.java:120)
    at org.jboss.ejb3.Ejb3Deployment.registerEJBContainer(Ejb3Deployment.java:301)
    at org.jboss.ejb3.Ejb3Deployment.start(Ejb3Deployment.java:362)
    at org.jboss.ejb3.Ejb3Module.startService(Ejb3Module.java:91)
    at org.jboss.system.ServiceMBeanSupport.jbossInternalStart(ServiceMBeanSupport.java:289)
    at org.jboss.system.ServiceMBeanSupport.jbossInternalLifecycle(ServiceMBeanSupport.java:245)
    at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:155)
    at org.jboss.mx.server.Invocation.dispatch(Invocation.java:94)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:86)
    at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
    at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:659)
    at org.jboss.system.ServiceController$ServiceProxy.invoke(ServiceController.java:978)
    at $Proxy0.start(Unknown Source)
    at org.jboss.system.ServiceController.start(ServiceController.java:417)
    at sun.reflect.GeneratedMethodAccessor9.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:155)
    at org.jboss.mx.server.Invocation.dispatch(Invocation.java:94)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:86)
    at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
    at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:659)
    at org.jboss.mx.util.MBeanProxyExt.invoke(MBeanProxyExt.java:210)
    at $Proxy33.start(Unknown Source)
    at org.jboss.ejb3.EJB3Deployer.start(EJB3Deployer.java:512)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:155)
    at org.jboss.mx.server.Invocation.dispatch(Invocation.java:94)
    at org.jboss.mx.interceptor.AbstractInterceptor.invoke(AbstractInterceptor.java:133)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:88)
    at org.jboss.mx.interceptor.ModelMBeanOperationInterceptor.invoke(ModelMBeanOperationInterceptor.java:142)
    at org.jboss.mx.interceptor.DynamicInterceptor.invoke(DynamicInterceptor.java:97)
    at org.jboss.system.InterceptorServiceMBeanSupport.invokeNext(InterceptorServiceMBeanSupport.java:238)
    at org.jboss.wsf.container.jboss42.DeployerInterceptor.start(DeployerInterceptor.java:87)
    at org.jboss.deployment.SubDeployerInterceptorSupport$XMBeanInterceptor.start(SubDeployerInterceptorSupport.java:188)
    at org.jboss.deployment.SubDeployerInterceptor.invoke(SubDeployerInterceptor.java:95)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:88)
    at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
    at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:659)
    at org.jboss.mx.util.MBeanProxyExt.invoke(MBeanProxyExt.java:210)
    at $Proxy34.start(Unknown Source)
    at org.jboss.deployment.MainDeployer.start(MainDeployer.java:1025)
    at org.jboss.deployment.MainDeployer.deploy(MainDeployer.java:819)
    at org.jboss.deployment.MainDeployer.deploy(MainDeployer.java:782)
    at sun.reflect.GeneratedMethodAccessor21.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.jboss.mx.interceptor.ReflectedDispatcher.invoke(ReflectedDispatcher.java:155)
    at org.jboss.mx.server.Invocation.dispatch(Invocation.java:94)
    at org.jboss.mx.interceptor.AbstractInterceptor.invoke(AbstractInterceptor.java:133)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:88)
    at org.jboss.mx.interceptor.ModelMBeanOperationInterceptor.invoke(ModelMBeanOperationInterceptor.java:142)
    at org.jboss.mx.server.Invocation.invoke(Invocation.java:88)
    at org.jboss.mx.server.AbstractMBeanInvoker.invoke(AbstractMBeanInvoker.java:264)
    at org.jboss.mx.server.MBeanServerImpl.invoke(MBeanServerImpl.java:659)
    at org.jboss.mx.util.MBeanProxyExt.invoke(MBeanProxyExt.java:210)
    at $Proxy9.deploy(Unknown Source)
    at org.jboss.deployment.scanner.URLDeploymentScanner.deploy(URLDeploymentScanner.java:421)
    at org.jboss.deployment.scanner.URLDeploymentScanner.scan(URLDeploymentScanner.java:634)
    at org.jboss.deployment.scanner.AbstractDeploymentScanner$ScannerThread.doScan(AbstractDeploymentScanner.java:263)
    at org.jboss.deployment.scanner.AbstractDeploymentScanner$ScannerThread.loop(AbstractDeploymentScanner.java:274)
    at org.jboss.deployment.scanner.AbstractDeploymentScanner$ScannerThread.run(AbstractDeploymentScanner.java:225)
21:33:12,203 INFO  [EJB3Deployer] Deployed: file:/C:/liang/jboss4.2/jboss-4.2.3.GA/server/default/deploy/HelloWorld.jar
21:33:12,203 ERROR [URLDeploymentScanner] Incomplete Deployment listing:

--- MBeans waiting for other MBeans ---
ObjectName: jboss.j2ee:jar=HelloWorld.jar,name=HelloWorldBean,service=EJB3
  State: FAILED
  Reason: java.lang.IllegalArgumentException: com.hongliang.ejb3.impl.HelloWorldBean is not an interface

--- MBEANS THAT ARE THE ROOT CAUSE OF THE PROBLEM ---
ObjectName: jboss.j2ee:jar=HelloWorld.jar,name=HelloWorldBean,service=EJB3
  State: FAILED
  Reason: java.lang.IllegalArgumentException: com.hongliang.ejb3.impl.HelloWorldBean is not an interface

***************************************************************************************

The following are the code

package com.hongliang.ejb3.impl;

import javax.ejb.Remote;
import javax.ejb.Stateless;

import com.hongliang.ejb3.HelloWorld;

@Stateless
@Remote(HelloWorldBean.class)
public class HelloWorldBean implements HelloWorld {

   
    public String sayHello(String name) {       
        return name + ": stupid EJB";
    }

}

_______________________________________________

package com.hongliang.ejb3;

public interface HelloWorld {
    public String sayHello(String name);
}

********************************************************************************************************