I was getting this error:
npm ERR! Darwin 15.2.0 npm ERR! argv "/Users/justin/.nvm/versions/node/v5.0.0/bin/node" "/Users/justin/.nvm/versions/node/v5.0.0/bin/npm" "shrinkwrap" npm ERR! node v5.0.0 npm ERR! npm v3.5.0 npm ERR! Problems were encountered npm ERR! Please correct and try again. npm ERR! extraneous: firstname.lastname@example.org /Users/justin/shakacode/react-webpack-rails-tutorial/client/node_modules/sleep npm ERR! npm ERR! If you need help, you may report this error at: npm ERR! <https://github.com/npm/npm/issues> npm ERR! Please include the following file with any support request: npm ERR! /Users/justin/shakacode/react-webpack-rails-tutorial/client/npm-debug.log
This fixed it for me:
npm uninstall --save-dev sleep && npm i --save-dev sleep && npm prune && npm shrinkwrap
Another thing to try is:
npm cache clean
And be sure you have relatively current versions of npm and maybe node.