Looks like your task service is not running.
When you run the ant script start.demo, once the build is successful, just take a look at the directory \jbpm-installer\jboss-as-7.1.1.Final\standalone\deployments\.
Once the .Deployed files for all the war files are generated, then try to run the example you have mentioned above. And see if the error still persists. Successful deployment of war file means that your task service has started. You dont need to explicitly start up human task service.
After successful deployment, Your directory should look like this :
https://community.jboss.org/servlet/JiveServlet/downloadImage/2-787698-20046/450-232/Untitled.png
The extension will keep changing before getting to .Deployed so wait for it to take its time. If for some reason, the extension changes to .Failed then you would need to figure out the reason for deployment failure.
Saludos
