I appear to be having the same problem. I was *also* having the problem of the navigation tree not loading, but I’ve now fixed that and I am still having issues with uploading.
It appears, looking at the apache error log, that the plugin is attempting to upload files to the root directory of my server and is being denied access (correctly). I even reset the permissions on / to test, and indeed, the file upload succeeded and the file was put in to the root directory. (I then cleaned that up.)
[Mon Nov 21 10:49:16.363566 2016] [proxy_fcgi:error] [pid 18952:tid 140059260995328] [client 192.168.101.134:62134] AH01071: Got error ‘PHP message: PHP Warning: move_uploaded_file(/ADB.txt): failed to open stream: Permission denied in /srv/www/itsmr/webroot/wp-content/plugins/media-library-plus/maxgalleria-media-library.php on line 388\nPHP message: PHP Warning: move_uploaded_file(): Unable to move ‘/tmp/phprVi5MC’ to ‘/ADB.txt’ in /srv/www/itsmr/webroot/wp-content/plugins/media-library-plus/maxgalleria-media-library.php on line 388\n’, referer: https://www.itsmr.org/wp-admin/admin.php?page=media-library
