Looks like the layer doesn't catch isUrgent as a missing method. Are you sure you loaded osx/cocoa.rb before?
Ah, as in I have a mixture of RubyCocoa code and MacRuby code from my last attempt. Could be. Doh! Yep. Ok, adding require 'osx/cocoa' Hmmm.... /Library/Frameworks/MacRuby.framework/Versions/0.3/usr/lib/ruby/1.9.0/ osx/rubycocoa.rb:52:in `instance_methods': stack level too deep (SystemStackError) from /Library/Frameworks/MacRuby.framework/Versions/0.3/usr/lib/ruby/ 1.9.0/osx/rubycocoa.rb:52:in `method_missing' from /Users/pierce/svnProjects/build/Release/Frictionless.app/ Contents/Resources/Action-mr.rb:847:in `isUrgent' from /Library/Frameworks/MacRuby.framework/Versions/0.3/usr/lib/ruby/ 1.9.0/osx/rubycocoa.rb:53:in `__super_objc_send__' from /Library/Frameworks/MacRuby.framework/Versions/0.3/usr/lib/ruby/ 1.9.0/osx/rubycocoa.rb:53:in `method_missing' from /Users/pierce/svnProjects/build/Release/Frictionless.app/ Contents/Resources/Action-mr.rb:847:in `isUrgent' from /Library/Frameworks/MacRuby.framework/Versions/0.3/usr/lib/ruby/ 1.9.0/osx/rubycocoa.rb:53:in `__super_objc_send__' from /Library/Frameworks/MacRuby.framework/Versions/0.3/usr/lib/ruby/ 1.9.0/osx/rubycocoa.rb:53:in `method_missing' from /Users/pierce/svnProjects/build/Release/Frictionless.app/ Contents/Resources/Action-mr.rb:847:in `isUrgent' ... 3083 levels... Pierce