Spring Controller Not Returning File

I have a simple Spring Controller setup to return a file (particularly a .CSV) via an AJAX Request. Here's my call which is utilizing YUI's framework which is making a standard XHR:

var downloadFile = Y.all('.downloadLink'); //traverses DOM for all downloadLink <a> tags
    downloadFile.on(
        'click',
        function(e){
            var fileName = e.currentTarget.attr('data-id');//retrieves file name
            Y.io.request(
            '/download/' + fileName, 
            {
                method: 'GET',
                on: {
                    success: function(e) {
                        alert('success');
                    },
                    failure: function(e) {
                        alert(e.type);
                    }
                 }
            });
    });

And here is my controller:

@RequestMapping( method = RequestMethod.GET, value = "/download/{fileName:.+}")
@ResponseBody
public FileSystemResource download(@PathVariable String fileName) throws IOException {
    File file = new File(rootPath + tempDir + '/' + fileName);
    try {
        if (file.exists()) {
            logger.info(fileName + " downloaded");
            return new FileSystemResource(file); 
        } else {
            logger.error("Could not download: " + fileName + " does not exist on server");
        }
    } catch (Exception e) {
        logger.error("Error Downloading File");
        e.printStackTrace();
    }
    return null;
}

As suggested in this question, I've tried forcing the download by modifying the method with

produces = MediaType.APPLICATION_OCTET_STREAM_VALUE

as well as including an HttpeServletResponse and setting the content type with

response.setContentType("application/force-download");

Without setting the MediaType, my request is successful and the @ResponseBody returns the contents of my file to the browser. However when I include the MediaType I receive a 406:

406 Not Acceptable: The resource identified by this request is only capable 
of generating responses with characteristics not acceptable according to the request "accept" headers.

I've searched the docs but I haven't found which "accepts" parameter I should be using to make this a valid request (if that alone would even resolve this issue). Any thoughts or suggested methods to retrieve my files? Cheers mates and Happy Easter

You need to set Accept header when you make a request. Never used YUI but try something like this

        Y.io.request(
        '/download/' + fileName, 
        {
            method: 'GET',
            on: {
                success: function(e) {
                    alert('success');
                },
                failure: function(e) {
                    alert(e.type);
                }
             }, 
            headers: {'Accept' : 'application/octet-stream'}
        });