Thank you for contacting us.
Sorry to hear about the bug when trying to delete a user and our team will do everything we can to help you get it working.
The error message you provided is generally returned by WordPress installations when there is something wrong with the PHP configuration on your web server.
I recommend reviewing your servers settings to make sure they meet the recommended configurations contained in this guide from our support center (https://www.boldgrid.com/support/troubleshooting/how-to-change-php-settings/).
Hopefully that helps you get this problem fixed, but please let us know if there is anything else that we can do to assist you.
Customer support service by UserEcho