Hi..we have configured the reverse proxy for our internal portal menu page for both kerberos and forms authentication mechanisms.  The failover to forms-auth is  working well in almost all exception scenarios.  

However, I have one exception that I'm trying to find a clean way to handle.  We're making use of user name mapping (LanidOrUidMapping) to hand users who's LANID is different from their ISAM UID.  This is working as long as the user has the LANID populated in the ISAM LDAP .  The exception I'm trying to handle is where a user does not have LANID populated.  This should not happen often but I'd still like to find a way to handle this.

What I'm finding in this scenario is that that failover to forms-auth doesn't occur.  Instead the user gets error code 0x13212065 at the browser.  I've tried creating a custom error for this code (i.e 13212065.html) and redirecting to the forms-auth login page.  What happens is the error (0x13212065) is persisting when the user submits username and password in the form (which is the login.html in same reverse proxy).

Is there a clean way to failover to forms-auth when the user doesn't have a valid lanid or UID to match their windows identity?