I recently updated our wiki from 1.26 to 1.31. I also updated the OS from Ubuntu 14.04 to Ubuntu 16.04 and from PHP 5 to PHP 7 in the process.
I am now unable to upload any file. I get the following message:
Could not open lock file for "mwstore://local-backend/local-public/b/b7/Images.jpg". Make sure your upload directory is configured correctly and your web server has permission to write to that directory. See https://www.mediawiki.org/wiki/Special:MyLanguage/Manual:$wgUploadDirectory for more information.
I have double checked the upload folder permissions (set for www-data with 755), checked the new PHP7 php.ini file to be sure it was set for file uploads to be allowed, and have the $wgUploadDirectory set for my images folder.
What else am I missing?