Module build failed: Error: ENOENT: no such file or directory, scandir 'D:\www\Demo\vue2.0-demos\node_modules\node-sass\vendor'
    at Object.fs.readdirSync (fs.js:896:18)
    at Object.getInstalledBinaries (D:\www\Demo\vue2.0-demos\node_modules\node-sass\lib\extensions.js:124:13)
    at foundBinariesList (D:\www\Demo\vue2.0-demos\node_modules\node-sass\lib\errors.js:20:15)
    at foundBinaries (D:\www\Demo\vue2.0-demos\node_modules\node-sass\lib\errors.js:15:5)
    at Object.module.exports.missingBinary (D:\www\Demo\vue2.0-demos\node_modules\node-sass\lib\errors.js:45:5)
    at module.exports (D:\www\Demo\vue2.0-demos\node_modules\node-sass\lib\binding.js:15:30)
    at Object.<anonymous> (D:\www\Demo\vue2.0-demos\node_modules\node-sass\lib\index.js:14:35)
    at Module._compile (module.js:569:30)
    at Object.Module._extensions..js (module.js:580:10)
    at Module.load (module.js:503:32)
    at tryModuleLoad (module.js:466:12)
    at Function.Module._load (module.js:458:3)
    at Module.require (module.js:513:17)
    at require (internal/module.js:11:18)
    at Object.<anonymous> (D:\www\Demo\vue2.0-demos\node_modules\sass-loader\lib\loader.js:3:14)
    at Module._compile (module.js:569:30)

Solution:
npm rebuild node-sass