If it’s the case that you just upgraded the node-sass package, the solution is often to simply rebuild node-sass.
Rebuild node-sass by entering the following in a CLI, positioned in the root of your web project, enter:

npm rebuild node-sass

Rebuild instructions in the Error

The solution is actually right there in the error message, however it’s easy to miss 🙁

The full error you get from building looks like this, but with “WebApp” replaced by the full path to your web app root.

WebApp\node_modules\node-sass\lib\index.js:15
    throw new Error(errors.missingBinary());
    ^

Error: Missing binding WebApp\node_modules\node-sass\vendor\win32-x64-48\binding.node
Node Sass could not find a binding for your current environment: Windows 64-bit with Node.js 6.x

Found bindings for the following environments:
  - Windows 64-bit with Node.js 6.x

This usually happens because your environment has changed since running `npm install`.
Run `npm rebuild node-sass` to build the binding for your current environment.
    at Object.<anonymous> (WebApp\node_modules\node-sass\lib\index.js:15:11)
    at Module._compile (module.js:556:32)
    at Object.Module._extensions..js (module.js:565:10)
    at Module.load (module.js:473:32)
    at tryModuleLoad (module.js:432:12)
    at Function.Module._load (module.js:424:3)
    at Module.require (module.js:483:17)
    at require (internal/module.js:20:19)
    at Object.<anonymous> (WebApp\node_modules\gulp-sass\index.js:187:21)
    at Module._compile (module.js:556:32)

Happy Coding! 🙂