by Juan Leyva.
You have to monitor the AJAX requests when you got this error, because it returns an error code/information
In Chrome, with the Developers tool open, go to Network. Enable the filter (click on the filter icon, and select XHR) there you can monitor every XHR request is sent to the server from the app so you can easily view in the Response tab the full error you got
Remember to enable in your Moodle installation the following: Admin / Development / Debugging / Show Developer erros and also check display errors checkbox