Even with bsf flag jruby lacks several classes needed for bsf (like org.jruby.javasupport.bsf.JRubyEngine). This classes are present in jruby-complete-1.4.0.jar from jruby home page. I'm using jruby 1.4.0-r5 Reproducible: Always
Fixed in 1.4.1-r1 and 1.5.1-r2.