Can you try visiting that resource directly, and see whether you get a “404” showing that the file is missing, or some other message.
If the file is missing, you can reinstall Wordfence without deleting its data — just uninstall the plugin, then install it and activate it again.
If you get a message that access to the file was blocked, do you have any additional blocking set up in .htaccess files, or by other plugins?
Otherwise, if you still have trouble, it might be best to reinstall Wordfence completely. To make sure the tables are recreated, turn on “Delete Wordfence tables and data on deactivation” near the bottom of the Options page. This will clear all of your settings and blocked IPs as well, but would give you a fresh start. If you want to keep your settings and most blocked IPs, you can use the export button at the bottom of the options page, before uninstalling, save the token that it gives you, then import it after reinstalling.
-Matt R