Rodrigo,
that's what is working for me. I have clean JBoss AS 5.1.0 installation with adjustments I explained above.
Are you still using 3.2.0.M2 or nightly version of JBossTools?
Do you get this exception in server console or eclipse log?
Check server/web/jmx-invoker-service.xml file if JNDI Name are defined in first node like
<mbean code="org.jboss.invocation.jrmp.server.JRMPProxyFactory"
name="jboss.jmx:type=adaptor,name=Invoker,protocol=jrmp,service=proxyFactory">
<!-- Use the standard JRMPInvoker from conf/jboss-service.xxml -->
<depends optional-attribute-name="InvokerName">jboss:service=invoker,type=jrmp</depends>
<!-- The target MBean is the InvokerAdaptorService configured below -->
<depends optional-attribute-name="TargetName">jboss.jmx:type=adaptor,name=Invoker</depends>
<!-- Where to bind the RMIAdaptor proxy -->
<attribute name="JndiName">jmx/invoker/RMIAdaptor</attribute>
...
</attribute>
<depends>jboss:service=Naming</depends>
</mbean>