If you use WPEngine for your webhosting, see THIS ANSWER
Some plugins activate a WordPress "Drop-in" plugin named advanced-cache.php, and do not remove it when you deactivate or delete the original plugin. Look in WordPress > Administration > Plugins and see if you see an entry for Drop-ins along the top of the page. Click on the word "Drop-ins" and see if the advanced-cache.php plugin is present:
If you know which plugin added the drop in plugin, you can deactive and delete it and see if it cleans up after itself. Unfortunately many plugins leave advanced-cache.php behind. You cannot delete it from the WordPress admin area. You need to use FTP or your control panel for your hosting account to find the file in the /wp-content/ folder and manually delete it. Ask your webmaster or webhost for help.