The merb-slices generator is relying on a merb's private API method: load_dependency. The method was modified in 1.0.4. Users should replace this line in their generated code with the public API version, which is:
dependency 'merb-slices', :immediate => true
merb -i still requires webrat
merb -i requires webrat
Fix:
gem uninstall addressable
remove the 2.x gem.