I had the same problem and I solved in this way:
You need to install or reinstall "bower"
Check your bower.json file, it should look something like this:
{
"name": "mean",
"version": "0.3.0",
"dependencies": {
"angular": "latest",
"angular-resource": "latest",
"angular-cookies": "latest",
"angular-mocks": "latest",
"angular-route": "latest",
"bootstrap": "latest",
"angular-bootstrap": "0.10.0",
"angular-ui-router": "#master"
}
}
and then run the following command:
sudo bower install --allow-root
This will install to "Angular" in the project