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.