The latest guvnor snapshot it is currently getting from the drools hudson build is unstable.
I'm working with them to get a new version of guvnor published, that should hopefully remove the errors you might be getting.
(I manually built a new version from the source code and that seems to work fine).
jBPM 5.0 final should be available at the end of this month, January 31st.
Kris