Generator not working?

[pietrop]

after installation running yo bootstrap and chosing css I get following error.

module.js:472
    throw err;
    ^

Error: Cannot find module 'internal/fs'
    at Function.Module._resolveFilename (module.js:470:15)
    at Function.Module._load (module.js:418:25)
    at Module.require (module.js:498:17)
    at require (internal/module.js:20:19)
    at evalmachine.<anonymous>:18:20
    at Object.<anonymous> (/usr/local/lib/node_modules/bower/node_modules/graceful-fs/fs.js:11:1)
    at Module._compile (module.js:571:32)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:488:32)
    at tryModuleLoad (module.js:447:12)