title: Tinymce-4 error: "File extension is not allowed " when inserting Excel(.xlsx) file in ASP.NET project
body: <p>I am using tinymce-4 plugin in my asp.net application. I have configured web.config file to allow '.xlsx' file to be uploaded like this:</p>
  
  <pre><code> &lt;setting name="AllowedFileExtensions" serializeAs="String"&gt;
      &lt;value&gt;'doc', 'docx', 'pdf', 'xls', 'xlsx', 'txt', 'csv','html','psd','sql','log','fla','xml','ade','adp','ppt','pptx'&lt;/value&gt;
    &lt;/setting&gt;
  </code></pre>
  
  <p>However, I am getting an error <strong>File extension is not allowed</strong>
  when inserting <strong>xlsx</strong> file.</p>
  
  <p>Am I missing something in my web.config file?</p>
  
  <p>Also, for initialization of plugin I am using the following code:</p>
  
  <pre><code> tfm_path = '/common/filemanager';
      tinymce.init({
          selector: 'textarea.html-editor',
          plugins: 'advlist anchor autolink charmap code contextmenu directionality fullpage fullscreen image insertdatetime link lists media pagebreak paste print searchreplace spellchecker table webizafilemanager wordcount',
          toolbar: "insertfile undo redo | styleselect | bold italic | alignleft aligncenter alignright alignjustify | bullist numlist outdent indent | link image",
          language: 'tr_TR'
      }); 
  </code></pre>