After an update to 2.5, the AD group used for authentication is not found. The specified principal was not found. Please make sure you have specified the correct Domain Controller address.
Our group is valid and is found 4 levels deep from the AD root. Perhaps this is the issue??
I see the requests going through the firewall to 2 local domain controllers and if I change to an IP address of a non-domain controller the error is different and does indicate a lack of connectivity to a domain controller.
Also, did the requirement for anonymous access ever get resolved?