Warble giving 'java.lang.NoClassDefFoundError: javax/servlet/ServletContext'?

Had a quick google, but can’t see why this is exploding
(trying to get the graylog2 rails app I was on about the other day
built) - any ideas?

graylog2-web-interface-0.9.6p1-RC1:$ jruby -S warble --trace
warble aborted!
load error:
/Users/sisred/Downloads/graylog2-web-interface-0.9.6p1-RC1/config/environment
– java.lang.NoClassDefFoundError: javax/servlet/ServletContext
org/jruby/RubyKernel.java:1033:in require' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/activesupport-3.1.3/lib/active_support/dependencies.rb:240:inrequire’
/Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/activesupport-3.1.3/lib/active_support/dependencies.rb:223:in
load_dependency' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/activesupport-3.1.3/lib/active_support/dependencies.rb:640:innew_constants_in’
/Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/activesupport-3.1.3/lib/active_support/dependencies.rb:639:in
new_constants_in' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/activesupport-3.1.3/lib/active_support/dependencies.rb:223:inload_dependency’
/Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/activesupport-3.1.3/lib/active_support/dependencies.rb:240:in
require' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/railties-3.1.3/lib/rails/application.rb:83:inrequire_environment!’
/Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/railties-3.1.3/lib/rails/application.rb:193:in
initialize_tasks' org/jruby/RubyProc.java:270:incall’
org/jruby/RubyProc.java:220:in call' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/task.rb:205:inexecute’
org/jruby/RubyArray.java:1615:in each' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/task.rb:200:inexecute’
/Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/task.rb:158:in
invoke_with_call_chain' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/1.8/monitor.rb:191:inmon_synchronize’
/Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/task.rb:151:in
invoke_with_call_chain' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/task.rb:144:ininvoke’
/Users/sisred/.gem/jruby/1.8/gems/warbler-1.3.4/lib/warbler/traits/rails.rb:29:in
before_configure' /Users/sisred/.gem/jruby/1.8/gems/warbler-1.3.4/lib/warbler/traits.rb:28:inbefore_configure’
org/jruby/RubyArray.java:1615:in each' /Users/sisred/.gem/jruby/1.8/gems/warbler-1.3.4/lib/warbler/traits.rb:28:inbefore_configure’
/Users/sisred/.gem/jruby/1.8/gems/warbler-1.3.4/lib/warbler/config.rb:170:in
initialize' /Users/sisred/.gem/jruby/1.8/gems/warbler-1.3.4/lib/warbler/task.rb:48:ininitialize’
/Users/sisred/.gem/jruby/1.8/gems/warbler-1.3.4/lib/warbler/application.rb:27:in
load_rakefile' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:65:inrun’
/Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:133:in
standard_exception_handling' /Users/sisred/Applications/jruby-1.6.7/lib/ruby/gems/1.8/gems/rake-0.9.2.2/lib/rake/application.rb:63:inrun’
/Users/sisred/.gem/jruby/1.8/gems/warbler-1.3.4/lib/warbler/application.rb:70:in
run' /Users/sisred/.gem/jruby/1.8/gems/warbler-1.3.4/bin/warble:11:in(root)’
org/jruby/RubyKernel.java:1058:in load' /Users/sisred/.gem/ruby/1.8/bin/warble:19:in(root)’
Tasks: TOP => environment
graylog2-web-interface-0.9.6p1-RC1:$