I have managed to bypass this error, to be precise complete step "install.examples.into.tomcat" by doing following steps:
1) reinstall/start Tomcat and make sure CATALINA_HOME was set to the right Tomcat installation ( in my case i have three Tomcat's on my comp for different software etc.. ); Yeah that's right, Tomcat is supposed to be stopped according to the guide - weird huh :-/
2) also i repeated the step "create.jbpm.schema" by calling ant from install dir
3) also steps: "install.examples.into.tomcat" and "load.example.identities"
4) I think I have restarted Tomcat at this point though I am not sure, but suffice to say that all ant build tasks done separately have succeeded.
I understand that these steps have little to no rationale behind them, but out of pure trial&error approach I gave it a try and who knew - it helped :-/
So far, I have yet to bypass another problem which is the empty list under the "Share repository" in jBPM Signavio designer - those objects you oght to drag and construct the diagram with are simply not there. I am going to analyze jBPM Developer's guide for clues, but it would be helpful if anyone could give me some insight to this matter?
Cheers,
Andrzej