If you see a PHP warning such as ""The following module is missing from the file system..." (or similar) on your site, this page explains how to fix it.
The warning was introduced in Drupal 7.40 (??? - @todo replace with correct version) and is displayed when Drupal is attempting to find a module in the file system, but either cannot find it or does not find it in the expected place. Usually this indicates a problem with your site. There are a few possible causes and corresponding solutions.