Your right. It seems to have something to do with the commons codec. But I really just used the jBPM pack ... I've tried it with the final-installer-full and the small final-installer and on a different (virtual) system as well. I have not changed anything on the installation, not even a process. But maybe I'm doing another mistake.
For this case, I try to explain what I'm doing (cannot believe that there is something wrong^^)
- Downloaded jbpm-5.2.0.Final-installer-full.zip (of course) and extracted it somewhere. e.g my home directory
- opened the directory jbpm in a terminal and ran "ant install.demo"
- started everything with "ant start.demo"
- Opened http://localhost:8080/jbpm-console in the browser and logged me in with krisv krisv
- went to processes->process overview
- the exception party started ;D
the next thing I'll try is to install it in a 32bit environment... because I'm running out of ideas^^