If you have many errors with Grunt in Vagrant and Windows this is probably due to symlinks.

To fix it :

1 – Add this lines in Vagrantfile

config.vm.provider "virtualbox" do |v|
    v.customize ["setextradata", :id, "VBoxInternal2/SharedFoldersEnableSymlinksCreate/vagrant", "1"]
end

2 – Run this command in an admin console on Windows

fsutil behavior set SymlinkEvaluation L2L:1 R2R:1 L2R:1 R2L:1

3 – And start your Vagrant

vagrant up

4 – Install Grunt globally

npm install -g grunt-cli
npm install -g grunt --no-bin-links

5 – Go in your project directory and install NPM Packages without errors

npm install --no-bin-links

6 – Use Grunt

grunt --version