Sorry to see you are having issues Nick!
Authentication error -851 is a known bug in some of our older Windows applications that has since been fixed. Make sure to update your Windows app in case you are using an older version and this is causing the issue. If this does not resolve your problem, please send an email to support@everykey.com and we would be happy to help you. Make sure to reference this review in your email so that our developers have context for your issue. Also, please make sure to include your OS version, Firefox version, and the version of the Everykey desktop application that you are using.
Thanks for catching the spelling error, we will fix it in the next release :)