Why does the following exception appear in the JON Agent log: Unable to connect to in-process ProfileService Caused by: NoInitialContextException

DEBUG [ResourceDiscoveryComponent.invoker.daemon-1] (org.rhq.plugins.jbossas5.InProcessJBossASDiscovery)- Unable to connect to in-process ProfileService.
java.lang.RuntimeException: Failed to lookup JNDI name 'java:ProfileService' from InitialContext.
     at org.rhq.plugins.jbossas5.connection.AbstractProfileServiceConnectionProvider.lookup(AbstractProfileServiceConnectionProvider.java:84)
     at org.rhq.plugins.jbossas5.connection.LocalProfileServiceConnectionProvider.doConnect(LocalProfileServiceConnectionProvider.java:47)
     at org.rhq.plugins.jbossas5.connection.LocalProfileServiceConnectionProvider.doConnect(LocalProfileServiceConnectionProvider.java:39)
     at org.rhq.plugins.jbossas5.connection.AbstractProfileServiceConnectionProvider.connect(AbstractProfileServiceConnectionProvider.java:42)
     at org.rhq.plugins.jbossas5.InProcessJBossASDiscovery.discoverInProcessJBossAS(InProcessJBossASDiscovery.java:71)
     at org.rhq.plugins.jbossas5.ApplicationServerDiscoveryComponent.discoverInProcessJBossAS(ApplicationServerDiscoveryComponent.java:261)
     at org.rhq.plugins.jbossas5.ApplicationServerDiscoveryComponent.discoverResources(ApplicationServerDiscoveryComponent.java:111)
     at sun.reflect.GeneratedMethodAccessor41.invoke(Unknown Source)
     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
     at java.lang.reflect.Method.invoke(Method.java:585)
     at org.rhq.core.pc.util.DiscoveryComponentProxyFactory$ComponentInvocationThread.call(DiscoveryComponentProxyFactory.java:266)
     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:269)
     at java.util.concurrent.FutureTask.run(FutureTask.java:123)
     at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
     at java.lang.Thread.run(Thread.java:595)
Caused by: javax.naming.NoInitialContextException: Need to specify class name in environment or system property, or as an applet parameter, or in an application resource file:  java.naming.factory.initial
     at javax.naming.spi.NamingManager.getInitialContext(NamingManager.java:645)
     at javax.naming.InitialContext.getDefaultInitCtx(InitialContext.java:247)
     at javax.naming.InitialContext.getURLOrDefaultInitCtx(InitialContext.java:284)
     at javax.naming.InitialContext.lookup(InitialContext.java:351)
     at org.rhq.plugins.jbossas5.connection.AbstractProfileServiceConnectionProvider.lookup(AbstractProfileServiceConnectionProvider.java:81)
     ... 15 more