The demo installer fails to on jBPM eclipse because it doesn't point to the Final version. I changed to use the following and it worked:
<target name="download.jBPM.eclipse"
....
Where did you get the installer?
As it seems jBPM 5.1 is fine:
https://github.com/droolsjbpm/jbpm/blob/5.1.0.Final/jbpm-installer/build.xml
The latest snapshot (master) is using the incorrect url however, so I'll correct this. Thanks for notifying.
Kris