Defender Class Not Found Error

Hi,

We are getting some strange errors with WP Defender on some sites. When WP-Defender is enabled, we cannot access wp-admin. We get the following error:

Fatal error: Class '@' not found in /home/sitename/public_html/wp-content/plugins/wp-defender/vendor/hammer/wp/settings.php on line 17

This has happened on several sites. The only way to get the wp-admin back is to disable the wp-defender plugin. The site was working fine and there have been no new plugins added or updated so not sure why this error is happening all of a sudden.

Can you please advise urgently?

Thanks