red5 server stream started but the flash client cannot play - red5

Question

What I want to achieve is that a user in the flash client calls a handler method defined in the red5 app which creates a server side stream and then plays it so that other users with flash client can view the broadcasted stream.
Here is my actionscript client side code triggered by a button click:
private function playLiveStream():void {
nc.call("remoteControl.playLiveStream", null, "demo_video.flv");
}
Here is my server side java code defined in a registered handler:
public void playLiveStream(String fileName) {
IScope scope=Red5.getConnectionLocal().getScope();
IServerStream stream=
StreamUtils.getServerStream(scope,"livestream1");
if (stream==null) {
stream=StreamUtils.createServerStream(scope, "livestream1");
StreamUtils.putServerStream(scope, "livestream1");
}
stream.addItem(SimplePlayItem.build(fileName));
stream.start();
}
Here is the actionscript to play the broadcasted stream:
ns = new NetStream(nc);
ns.play("livestream1");
However, in flash client, the stream plays for only one second and then stopped.
If I click the button to call the handler method again, there is error in the java log. Here is my java log for the error:
java.lang.reflect.InvocationTargetException: null
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_25]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_25]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_25]
at java.lang.reflect.Method.invoke(Method.java:483) ~[na:1.8.0_25]
at org.red5.server.service.ServiceInvoker.invoke(ServiceInvoker.java:193) [red5-server-common-1.0.6-RELEASE.jar:na]
at org.red5.server.service.ServiceInvoker.invoke(ServiceInvoker.java:115) [red5-server-common-1.0.6-RELEASE.jar:na]
at org.red5.server.net.rtmp.RTMPHandler.invokeCall(RTMPHandler.java:186) [red5-server-common-1.0.6-RELEASE.jar:1.0.6-RELEASE]
at org.red5.server.net.rtmp.RTMPHandler.onCommand(RTMPHandler.java:293) [red5-server-common-1.0.6-RELEASE.jar:1.0.6-RELEASE]
at org.red5.server.net.rtmp.BaseRTMPHandler.messageReceived(BaseRTMPHandler.java:105) [red5-server-common-1.0.6-RELEASE.jar:1.0.6-RELEASE]
at org.red5.server.net.rtmp.ReceivedMessageTask.call(ReceivedMessageTask.java:63) [red5-server-common-1.0.6-RELEASE.jar:1.0.6-RELEASE]
at org.red5.server.net.rtmp.ReceivedMessageTask.call(ReceivedMessageTask.java:14) [red5-server-common-1.0.6-RELEASE.jar:1.0.6-RELEASE]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_25]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [na:1.8.0_25]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_25]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_25]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_25]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_25]
Caused by: java.lang.IllegalStateException: State STOPPED not valid to start
at org.red5.server.stream.ServerStream.start(ServerStream.java:428) ~[red5-server.jar:1.0.6-RELEASE]
at com.eeplace.red5.core.RemoteControlHandler.playLiveStream(RemoteControlHandler.java:144) ~[classes/:na]
... 17 common frames omitted
Did anyone encounter the same error before?
Thank you for any suggestion.