npm packages from devDependencies to dependencies not working-Collection of common programming errors

I’m trying to deploy an app based on grunt with heroku.

One need I have is to let heroku install all npm packages. For this reason I decided to update package.json and to move everything from devDependencies to dependencies. I then run npm install and as far as all libraries are the same, I expect evrything to be working, but it doesn’t.

  • package.json with all packages into devDependencies (WORKING)
  • package.json with all packages into dependencies (NOT WORKING)

The error I get is this

Loading "Gruntfile.js" tasks...ERROR
>> TypeError: Cannot set property 'name' of undefined
Warning: Task "server" not found. Use --force to continue.

This does not make any sense to me. Do you have any hint about?