Unspecified "error" event. (Incorrect arguments)

For some reason I am getting this error when I try to login to my application: "unspecified "error" event. (Incorrect arguments)"

This only happens when I attempt to login so I'm assuming there's an error somewhere in my login function and or user Schema.

    var userSchema = new mongoose.Schema({
        username:   String,
        password:   String,
        datapoint:  String,
        email:      String,
        resetPasswordToken: String,
        resetPasswordExpires: Date
    });



    userSchema.pre('save', function(next) {
      var user = this;
      if (!user.isModified('password')) return next();
      bcrypt.genSalt(10, function(err, salt) {
        if (err) return next(err);
        bcrypt.hash(user.password, salt, null, function(err, hash) {
          if (err) return next(err);
          user.password = hash;
          next();
        });
      });
    });

    userSchema.methods.comparePassword = function(password) {
      return bcrypt.compareSync(password, this.password);
    }


app.post('/login', passport.authenticate('local-login', {
  successRedirect: '/',
  failureRedirect: '/login',
}));

 passport.use('local-login', new LocalStrategy({
  usernameField: 'username',
  passwordField: 'password',
  passReqToCallback: true
}, function(req, username, password, done) {
  User.findOne({ username: username}, function(err, user) {
    if (err) return done(err);

    if (!user) {
      return done(null, false, req.flash('error', 'No user has been found'));
    }

    if (!user.comparePassword(password)) {
      return done(null, false, req.flash('error', 
        'Wrong password. Please check Caps Lock button, capital letters and retype the password.'));
    }
    return done(null, user);
  });
}

));

via AndrewLeonardi