I do not know what may be wrong with your code (besides the initial line does not compile in my environment). Anyway the code works fine as below (JBoss-3.2.0-Beta)

InitialContext ctx = new InitialContext();
Object o = ctx.lookup("ejb/mgmt/MEJB");
ManagementHome home = (ManagementHome)PortableRemoteObject.narrow(o, ManagementHome.class);
Management mejb = home.create();

String domain = mejb.getDefaultDomain();
ObjectName objName = new ObjectName(domain+":"+"j2eeType=EJBModule,*");
Set names = mejb.queryNames(objName, null);
Iterator itr = names.iterator();
while(itr.hasNext()) {
ObjectName name = (ObjectName)itr.next();
System.out.println("EJBModule: " + name);
String strKeyProperty = name.getKeyPropertyListString();
System.out.println("EJBProps : " + strKeyProperty);
ObjectName[] ejbs = (ObjectName[])mejb.getAttribute(name, "EJBs");
}