jquery ajax success event handler not getting called with Node.js/express

My ajax succes event handler is not getting called.

I use backbone as my clientside MVC This is how i set my ajax function:

$.ajax({
          type: "POST"
        , url: "/image-delete"
        , data: { "imageName" : "someImage.jpg" }
        , success: function(response) {
            console.log("succes = ", response);
            self.model.get('pictures').splice(imageName, 1);
            $(event.currentTarget).closest('.picture-frame').remove();
            console.log(self.model);
          }
        , error: function(response) {
            utils.showAlert('Error', 'An error occurred while deleting this picture', 'alert-error');
          }

And this is the serverside with node.js/express:

exports.deleteImage = function(req, res) {

    console.log("Deleting image ", req.body.imageName);
    var filePath = "./private/uploads/" +  req.body.imageName;

    fs.unlink(filePath, function(err) {
        if(err){
            console.log("error with deleting:", err);
        } else {
            console.log("succesfull deleted");
            res.set({'Content-Type': 'text/plain'});
            res.send("succesfull deleted");
            res.end();
        }
    }); 

}

The file is succesfull deleted and in my terminal i get the message "succesfull deleted" so the "else" function in node is fired, but the succes of the ajax function is nog called...