Maybe your birt zip file was not downloaded fully? In $jbpm-installer-dir/build.properties you can set
jBPM.birt.download=true
and then run
ant clean.demo
ant install.demo
ant start.demo
This should install the birt runtime in $jbpm-installer-dir/$jboss-as/server/default/data directory correctly.
Regarding >> but it didn't work <<
You are going to have to be a little more specific on this one ;)
Hope this helps.