The error "PHP Warning: mkdir(): Permission denied in wp-content/plugins/swift-framework/includes/options/redux-framework/inc/class.redux_filesystem.php" found in an error_log file or "File Permission Issues - We were unable to modify required files.
Please ensure that wp-content/uploads/ has the proper read-write permissions, or modify your wp-config.php file to contain your FTP login credentials as outlined here.." found within the WordPress admin interface can occur when your wp-contents, wp-contents/uploads, wp-contents/uploads/redux folders are not set to 755 or the path you have defined under WordPress, settings, media is set to an invalid path. Change back to wp-content/uploads, save and the field will disappear and be set back to the default and should work properly again!