Spring Controller Not Returning File

I have a simple Spring Controller setup to return a file:

@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