This is kinda confusing. I have set up authentication to all of my Cisco network switches using AD authentication via Cisco ACS v4.0. and it worked great until I upgraded all of my DCs to Windows 2008. Now I get a user name and password failed for some reason the authentication does not work anymore. I checked the Cisco event logs and all I see for failed attempts is "Internal Error". Has anyone heard of any sort of issue with Windows 2008 and Cisco ACS? Prior to the upgrade we were running Windows 2003 DCs in a Windows 2003 Native mode forest. We have not upgraded to 2008 native mode so for all intents and purposes it should function the same. Right??? I guess Im missing something so any help would be appreciated.