Plugin stops registered users from login

Hi, this afternoon, two users on reichweite.de can’t login anymore with the message “Access Denied
This site is protected by the Stop Spammer Registrations Plugin.
If you feel that you have been blocked in error, you may notify the Admin and ask to placed on the system white list. This site’s admin will be notified and can review the reason why you were blocked.”

1. I added their email addresses to the whitelist – still no login
2. I deactivated the plugin – login possible

What do I have to do to reactivate the plugin?

Michael

https://wordpress.org/plugins/stop-spammer-registrations-plugin/