JON UI fails to load metrics with the message "Cannot load metrics" while plugin container is restarting

Issue

• JON UI fails to load metrics with the message "Cannot load metrics" while plugin container is restarting
• Our server.log showed the following error:

07:52:45,040 ERROR [org.rhq.enterprise.communications.command.client.ClientCommandSenderTask] (http-/0.0.0.0:7080-16) {ClientCommandSenderTask.send-failed}Failed to send command [Command: type=[remotepojo]; cmd-in-response=[false]; config=[{rhq.security-token=fVOGVTEmF+SNLHk32nOm/xn/KisSwnV6AhEyLqP5Uz3Axtru8W2aUWc5pMKH8xtLOvc=, rhq.timeout=5000, rhq.send-throttle=true}]; params=[{invocation=NameBasedInvocation[ping], targetInterfaceName=org.rhq.enterprise.communications.Ping}]]. Cause: java.util.concurrent.TimeoutException:null. Cause: java.util.concurrent.TimeoutException
07:52:55,050 ERROR [org.jboss.as.ejb3.invocation] (http-/0.0.0.0:7080-22) JBAS014134: EJB Invocation failed on component MeasurementDataManagerBean for method public abstract java.util.Set org.rhq.enterprise.server.measurement.MeasurementDataManagerRemote.findLiveData(org.rhq.core.domain.auth.Subject,int,int[]): javax.ejb.EJBException: java.lang.reflect.UndeclaredThrowableException
...
    at org.rhq.enterprise.server.measurement.MeasurementDataManagerLocal$$$view123.findLiveData(Unknown Source) [rhq-server.jar:4.9.0.JON320GA-redhat-2]
    at org.rhq.coregui.server.gwt.MeasurementDataGWTServiceImpl.findLiveData(MeasurementDataGWTServiceImpl.java:85)
...
Caused by: java.lang.reflect.UndeclaredThrowableException
    at com.sun.proxy.$Proxy5638.getRealTimeMeasurementValue(Unknown Source)
    at org.rhq.enterprise.server.measurement.MeasurementDataManagerBean.findLiveData(MeasurementDataManagerBean.java:892) [rhq-server.jar:4.9.0.JON320GA-redhat-2]
    at org.rhq.enterprise.server.measurement.MeasurementDataManagerBean.findLiveData(MeasurementDataManagerBean.java:858) [rhq-server.jar:4.9.0.JON320GA-redhat-2]
...
Caused by: java.lang.NoSuchMethodException: There is no remote POJO that can service the method invocation request. Command: Command: type=[remotepojo]; cmd-in-response=[false]; config=[{rhq.security-token=fVOGVTEmF+SNLHk32nOm/xn/KisSwnV6AhEyLqP5Uz3Axtru8W2aUWc5pMKH8xtLOvc=, rhq.send-throttle=true}]; params=[{targetInterfaceName=org.rhq.core.clientapi.agent.measurement.MeasurementAgentService, invocation=NameBasedInvocation[getRealTimeMeasurementValue]}]
...

• When attempting to see metrics in JON UI we got blank screen and message "Cannot load metrics" is shown.