May be something with your lookup name is wrong.
Have a look at your JBoss log file after your EJB has been deployed.
There you can see the JNDI bindings of your EJB.
JBoss7 EJB lookup Name
context.lookup("ejb:" + appName + "/" + moduleName + "/" + distinctName + "/" + beanName + "!" + viewClassName);
This is my lookup name as example:
"ejb:/MtzWebComm//CommEJB!de.miditec.communication.ejb.CommEJBHome";
appName : Empty String
moduleName : MtzWebComm
distinctName : Empty String
beanName : CommEJB
viewClassName: de.miditec.communication.ejb.CommEJBHome