Hi Hui!
I think you are trying to put your .bpmn files in a wrong place. If you edit your build.xml file, you'll find the following line within the "Start JBoss AS" target:
<arg value="-Djbpm.console.directory=${install.home}/sample/evaluation/src/main/resources" />
If you leave it that way, then you'll have to put the .bpmn files into jbpm-installer/sample/evaluation/src/main/resources. However, I think it is better to change the path to a more convenient directory.
Apart from that, I must say I'm not able to load all the processes I make. I can only load "simple" processes. If I try to load more "complex" processes I also get HTTP 500 errors...
Good luck!
Rafa.