You are most likely running the Guvnor version provided in the jBPM5.0 installer. Note that some changes in the Guvnor code were needed to get the standalone editor feature working with the designer, and those were post-jBPM5.0. You can either build Guvnor from master ( https://github.com/droolsjbpm/guvnor ) and replace your drools-guvnor.war with the one you build, or wait for jBPM5.1 which will include the updates.
Thanks.