I have looked around at other people having this issue but haven't seen a definite answer.
I installed elFinder 2.1.28 and renamed the connector files. I get this error saying,
"Invalid backend response.
Data is not JSON."
With the contents of the connector files displayed after the error message. Here is a screenshot,

Thanks,
Cam
Elfinder run only in server which can simulate php functions. Not directly run simple double click on elFinder.Src.Html if you on windows platform you must download wamp server or xamp application to simulate php functions.
Server
Any web server
PHP 5.2+ (Recommend PHP 5.4 or higher)
I think this must help for you.
That error massage is show that connector.minimal.php dosen't simulate correctly in your server.
Wow cannot believe I forgot to install php I feel like an idiot.
Thanks. That was the issue.