NetworkError: 404 Not Found

I too faced the same issue.

The solution that worked for me is as follows:
In the fileupload administration page update the for Base URL to load YUI Javascript Libraries: to
http://yui.yahooapis.com/combo?2.7.0/build

Please find the patch for the filedepot page.tpl.php
The filepath is:
/sites/all/modules/contrib/filedepot/theme/page.tpl.php

20<!-- On-Demand loading the Module Javascript using YUI Loader -->
21
-22<script type="text/javascript" src="<?php print $yui_base_url ?>yuiloader/yuiloader.js"></script>
+22<script type="text/javascript" src="<?php print $yui_base_url ?>/yuiloader/yuiloader.js"></script>
23<script type="text/javascript">

55<script type="text/javascript">
-56  var YUIBaseURL  = "<?php print $yui_base_url ?>"/;
-56  var YUIBaseURL  = "<?php print $yui_base_url ?>";
57</script>

This made me going...:)