Yes, I believe the issue is around the true
line in the XML file.

This produces an exception. I believe there is a fix but I do not know how to access the fix (something about the JVMRouteFilter class failing because its referring to an Abstract class rather than a "regular" class, but I don't know how to obtain the Java class and rebuild it with the fixes.
Does anyone know how to do this?

Sorry the line I cut and pasted didn't come through apparently. Its the
true

line.

Damn it still didn't come through. I guess its illegal to put XML in these entries! Here goes again:

attribute="UseJK" true

Yes:

Yes on the Sourceforge site:
[ 1037726 ] JvmRouteFilter crashes in init() method for clustered webapp
Bug details:

During JBoss startup JvmRouteFilter.init() method
throws an exception
"JvmRouteFilter.init(): No AbstractJBossManager found
for clustering support."

this happens because the code

...
manager_ = (AbstractJBossManager)
filterConfig.getServletContext().getAttribute(AbstractJBossManager.class.getName());
...

returns null, there is no object registered with the key
"org.jboss.web.tomcat.tc5.session.AbstractJBossManager"

the manager is registered under key
"org.jboss.web.tomcat.tc5.session.JBossManager"

Thanks Jerry:
I have resolved the issue. Our problem was that we couldn't use anything but version 4.0.0 so I obtained the patch for the JvmRouteFilter class, plugged it into the JAR file and it worked!