Generally DuplicateServiceException  means you are trying to deploy the same service twice with the same JNDI name [java.global.app.appEJB."InvitationBean!org.app.core.InvitationLocal"] ,  Attaching complete server log will reveal more informations.

Also it is confusing that in thread title you mentioned  JBoss AS 7.1.1 but in the description of the issue you mentioned JBoss AS 6 ?

From your logs i see two isses:

Issue : 1   I see that at time "11:13:30" the EJB was registered successfully ,  but after a second (11:13:31) looks like container might have found another copy of the same classes from some other JARs may be from "EAR/lib"  (just a guess)

2014-12-04 11:13:30,435 INFO  [org.jboss.as.ejb3.deployment.processors.EjbJndiBindingsDeploymentUnitProcessor] (MSC service thread 1-5) JNDI bindings for session bean named InvitationBean in deployment unit subdeployment "appEJB.jar" of deployment "app.ear" are as follows:

    java:global/app/appEJB/InvitationBean!org.app.core.InvitationLocal
    java:app/appEJB/InvitationBean!org.app.core.InvitationLocal
    java:module/InvitationBean!org.app.core.InvitationLocal
    java:global/app/appEJB/InvitationBean
    java:app/appEJB/InvitationBean
    java:module/InvitationBean
.
.
.
.
2014-12-04 11:13:31,953 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-7) MSC00001: Failed to start service jboss.deployment.subunit."app.ear"."appEJB.jar".INSTALL: org.jboss.msc.service.StartException in service jboss.deployment.subunit."app.ear"."appEJB.jar".INSTALL: Failed to process phase INSTALL of subdeployment "appEJB.jar" of deployment "app.ear"
    at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:119)
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1811)
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1746)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
Caused by: org.jboss.as.server.deployment.DeploymentUnitProcessingException: JBAS011058: Failed to install component InvitationBean
    at org.jboss.as.ee.component.deployers.ComponentInstallProcessor.deploy(ComponentInstallProcessor.java:100)
    at org.jboss.as.server.deployment.DeploymentUnitPhaseService.start(DeploymentUnitPhaseService.java:113)
    ... 5 more
Caused by: org.jboss.msc.service.DuplicateServiceException: Service jboss.naming.context.java.global.app.appEJB."InvitationBean!org.app.core.InvitationLocal" is already registered
    at org.jboss.msc.service.ServiceRegistrationImpl.setInstance(ServiceRegistrationImpl.java:154)
    at org.jboss.msc.service.ServiceControllerImpl.startInstallation(ServiceControllerImpl.java:227)
    at org.jboss.msc.service.ServiceContainerImpl.install(ServiceContainerImpl.java:560)
    at org.jboss.msc.service.ServiceTargetImpl.install(ServiceTargetImpl.java:201)
    at org.jboss.msc.service.ServiceControllerImpl$ChildServiceTarget.install(ServiceControllerImpl.java:2228)
    at org.jboss.msc.service.ServiceTargetImpl.install(ServiceTargetImpl.java:201)
    at org.jboss.msc.service.ServiceControllerImpl$ChildServiceTarget.install(ServiceControllerImpl.java:2228)
    at org.jboss.msc.service.ServiceBuilderImpl.install(ServiceBuilderImpl.java:307)
    at org.jboss.as.ee.component.deployers.ComponentInstallProcessor.deployComponent(ComponentInstallProcessor.java:182)
    at org.jboss.as.ee.component.deployers.ComponentInstallProcessor.deploy(ComponentInstallProcessor.java:93)
    ... 6 more

Can you check if inside your EAR you have multiple copies of the class "InvitationLocal" or "InvitationBean"  ?

Issue: 2  The following NullPointerException indicates a Bug in JBoss Which is addressed as part of  [WFLY-2221] NPE in BinderService - JBoss Issue Tracker     (fixed in WildFly 8.0)  The code was not written properly to handle a scenario when the "controller"  becomes null. 

2014-12-04 11:13:34,382 ERROR [org.jboss.msc.service] (MSC service thread 1-4) MSC00002: Invocation of listener "org.jboss.as.ee.component.deployers.ModuleJndiBindingProcessor$BinderReleaseListener@6e40d18f" failed: java.lang.NullPointerException
    at org.jboss.as.naming.service.BinderService.release(BinderService.java:81)
    at org.jboss.as.ee.component.deployers.ModuleJndiBindingProcessor$BinderReleaseListener.transition(ModuleJndiBindingProcessor.java:300)
    at org.jboss.msc.service.ServiceControllerImpl.invokeListener(ServiceControllerImpl.java:1416)
    at org.jboss.msc.service.ServiceControllerImpl.access$2700(ServiceControllerImpl.java:49)
    at org.jboss.msc.service.ServiceControllerImpl$ListenerTask.run(ServiceControllerImpl.java:1954)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)

Hello,

This error is due to the presence of old deployed EAR. try to delete <deployments></deployments> in you standalone file and also remove deployments file (on your server, right clic, show in , file browser, delete all) and then restard your server and deploy you EAR.