In my previous post, I wrote about my struggle over an application on Google App Engine that uses JRuby's builtin library, yaml. I found the reason of the error at JRUBY-3892. Builtin library needs jruby.home environment variable to be set correctly, and it should be done in jruby-complete.jar. But, jruby-complete.jar built from old JRuby 1.4.0dev had a somewhat broken path. Since the issue has been resolved in the end of Auguest, I tried again using the latest JRuby 1.4.0dev cloned out from git repo. It worked. So, the final release of JRuby 1.4.0 won't have this problem.
Now, my sample Servlet, ParsenRunServlet is working at http://servletgarden-in-red.appspot.com/. If you are interested in the code, those are in JRuby Embed API Wiki.