title: Valums file uploader plugin shows upload failed message each time
body: <p>I am using <code>valum file uploader</code>. The js code for initializing plugin is:</p>
  
  <pre><code>function Initializer() {
      var uploader = new qq.FileUploader({
          element: document.getElementById('file-uploader'),
          action: '/_Image/Upload',
          params: {},
          allowedExtensions: ['jpg', 'jpeg', 'png', 'gif'],
          debug: true,
          onSubmit: function (id, fileName) { },
          onProgress: function (id, fileName, loaded, total) { },
          onComplete: function (id, fileName, responseJSON) { },
          onCancel: function (id, fileName) { },
          onError: function (id, fileName, xhr) { },
  
          messages: {
              typeError: "{file} has invalid extension. Only {extensions} are allowed.",
              sizeError: "{file} is too large, maximum file size is {sizeLimit}.",
              minSizeError: "{file} is too small, minimum file size is {minSizeLimit}.",
              emptyError: "{file} is empty, please select files again without it.",
              allowedExtensionsError : "{file} is not allowed.",
              onLeave: "The files are being uploaded, if you leave now the upload will be cancelled."
          },
          showMessage: function (message) {
              alert(message);
          }
      });
  }
  </code></pre>
  
  <p>The file is successfully uploaded on the server but the plugin is showing the <code>file uplode fail</code> message each time.
  What's the issue?</p>