Social Articles Issues

Hello! I’ve activated Social Articles, but unfortunately I can’t get images to upload for admin or subscribers. I wait for minutes but the upload never ends. The developer of this plugin is not responsive at all and I don’t know what else to do.

Here are the errors I get when I inspect the page. I hope this is useful:

SUBSCRIBER ACCOUNT (MOZILLA)
TypeError: o is null isotope.pkgd.min.js:7:6985
SyntaxError: JSON.parse: unexpected character at line 4 column 2 of the JSON data jquery.js:5:15990
Empty string passed to getElementById(). jquery.js:2:0
Use of getPreventDefault() is deprecated. Use defaultPrevented instead. load.sumome.com:

ADMIN ACCOUNT (CHROME)
Mixed Content: The page at ‘https://site.com/community/member1/articles/new/’ was loaded over HTTPS, but requested an insecure stylesheet ‘http://yui.yahooapis.com/2.9.0/build/reset/reset-min.css’. This request has been blocked; the content must be served over HTTPS.
‘Range.detach’ is now a no-op, as per DOM (http://dom.spec.whatwg.org/#dom-range-detach).
https://site.com/wp-content/plugins/social-articles/upload-handler.php Failed to load resource: the server responded with a status of 404 (Not Found)
site.com/:4 Uncaught SyntaxError: Unexpected token <
https://site.com/wp-content/plugins/social-articles/upload-handler.php Failed to load resource: the server responded with a status of 404 (Not Found)