Invalid backend response. Data is not JSON.

Try to access /elfinder/connector url and check if there any error messages

I have the same issue and accessing /elfinder/connector gives me:
Fatal error: Call to undefined method elFinderDrupal::getNetVolumes() in /var/www/sites/all/modules/contrib/elfinder/inc/elfinder.drupal.inc on line 28

Try to use latest library

http://sourceforge.net/projects/drupal-elfinder/files/Library/elfinder-l...

Seems like that worked, thanks a lot!

Calling "/elfinder/connector" shows me:

Fatal error: Declaration of elFinderVolumeDrupal::_save() must be compatible with elFinderVolumeDriver::_save($fp, $dir, $name, $mime, $w, $h) in /Applications/MAMP/htdocs/100_Projects/relevantiveIntranet/sites/default/modules/filefield-modules/elfinder/inc/elfinder.drupalfs.driver.inc on line 469


Library is the latest one.

The attached combination works for me.

elFinder 2.x library have changed api. You should use dev library build for latest dev module. Dev library can be downloaded there:

http://sourceforge.net/projects/drupal-elfinder/files/Library/

hey, this patch will fix this bug

~ Almog Baku

#8 works for me.
But I am surprised to find that there seems a script to upload dev version to http://sourceforge.net/projects/drupal-elfinder/files/Library/ every 2 hours. It's wasting resources.

To avoid issue please use latest library which you can get from SourceForge. #9 applicable if you strictly need to use existing library version since it rolling back elFinder to old library api ($mime, $w and $h arguments replaced by $stat array).