Updating Mongoose model using express.js, running into model validation errors. How to avoid?

I am trying to update a user model using Mongoose. The update I want to do is to simply update the user's editor_score/writer_score. However, I keep getting a validation error because of my email. Whenever I have my service PUT to the server the information of the model thats been changed, I continually run into this error:

{"error":{"message":"Validation failed","name":"ValidationError","errors":{"email":{"message":"E-mail address is already in-use","name":"ValidatorError","path":"email","type":"user defined","value":"test@test.com"}}}}

my updateUser method looks like this:

    exports.updateUser = function(req, res){
        var userId = req.params.userId;
       User.findOne({_id: mongoose.Types.ObjectId(userId)}).exec(function(error, oneUser){

        if(error){
            return res.jsonp(500, {
                error: error
            });
        }
        oneUser = _.extend(oneUser, req.body);
        oneUser.save(function(err) {
        if (err) {
            return res.jsonp(500, {
                error: err
            });
        }
        res.jsonp(oneUser);



     });
    });
};

How can I avoid this validation error? Am I even allowed to update a user who isn't logged on? My goal is to update other user's editing/writing scores based on other user's discretion. Any insight would be extremely helpful, been working on this. Thanks