If you are using NPM or Grunt on Windows and are having issues running your tasks it would pay to check the file encoding on your package.json file. I was receiving the following error while trying to run Grunt:

"Warning: C:\dev\project\package.json : Unexpected token ? Use --force to continue."

The issue happened to be that VisualStudio had sneakily saved the file as UTF8-BOM, changing the encoding to UTF8 without the BOM solved this. I found the NPM bug which has been closed without a fix. Hopefully this will allow you to solve this quicker than I did!