"error decoding the response sent by the server" occurs when the Javascript interface does not recognize the response sent from the server as valid JSON or a CodeIgniter error page. It would most commonly be caused by the server returning a blank page when there is an internal server error and PHP is not set to display errors.
If the above suggestion does not cause a more descriptive error message to be displayed in the browser or the error log, you can try this to see exactly what the server is sending:
Are you familiar with Chrome Developer Tools or the Mozilla Web Console? In either Chrome or Mozilla Firefox, bring up the "Paths" page. Right click somewhere in the page header and choose "Inspect Element". This will open the Chrome Developer Tools or the Mozilla Web Console. Click the "Network Tab" which shows requests made to the server. Hit the "Refresh" button on the paths page and you should see one or both of those requests come up in the Network tab of the Chrome Developer Tools or the Mozilla Web Console.
Most likely one of them is not returning 200 as the status... Maybe a 500 error? You can click the request in Chrome Developer Tools or the Mozilla Web Console to get more information. Look at the response. It should be JSON. Is it an error? Is it blank?
