Error: Cannot find module 'etag'

[Elena Lenskė]

module.js:487
throw err;
^

Error: Cannot find module 'etag'
at Function.Module._resolveFilename (module.js:485:15)
at Function.Module._load (module.js:437:25)
at Module.require (module.js:513:17)
at require (internal/module.js:11:18)
at Object. (C:\Users\Developer\Desktop\Projects\pure-aqua\node_modules\express\node_modules\send\index.js:21:12)
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)

How to sort this issue? It keeps reocurring.