Hi,
I checked the forum, but non of the anserws solved my problem:
I Use Joomla 3.4.8, latest K2 2.6.9
K2 ran fine up to today, when message Invalid backend response.
Data is empty poped up in K2 mediamanager.

I turned of reports, added // to $this->_checkArchivers(); in elfinder...to no effect.
What am I missing?
Thanks for yiour help

Hi,

Probably something is breaking the server's JSON response. Try to use the browser development tools to see the response that comes from the server.