jBPM 4.3 distro is prepared for jBOSS AS 5.0.0.GA Because you are installing in jBOSS AS 4.2.3.GA you have to do some modifications.
Change <jbpm-distro-home>\install\src\jboss\config\deploy\jbpm\jbpm-destinations-service.xml to fix for 4.2.3.GA:
<mbean code="org.jboss.mq.server.jmx.Queue"
name="jboss.mq.destination:service=Queue,name=JbpmCommandQueue">
<depends optional-attribute-name="DestinationManager">
jboss.mq:service=DestinationManager
</depends>
</mbean>
And run the ant target "install.jbpm.into.jboss" again.
Optionally edit the file directly on jBOSS at <jboss-home>\server\default\deploy\jbpm\jbpm-destinations-service.xml and insert the same modifications.