SSL VPN Error Codes

Anybody manage to compile a list of error code descriptions?  We use, mostly, FortiClient 6.4 with an external MFA provider (PrivacyIDEA).  Anytime there is a connection issue, we get the error message, 'The server you want to connect to requests identification, please choose a certificate and try again' followed by an error code in parenthesis.  This is incredibly frustrating, especially when the uninitiated starting asking about certificates when the actual issue is the user entered their password wrong or they failed host checking.  Globally, cert checking is disabled, though we have a couple portals that have cert checking enabled, this error is displayed on all of them.