Hi everyone! A few weeks ago we moved our Mailbox-, Hub Transport- and Client Access Server Role from Windows 2003 SP2 Exchange 2007 SP1 (+ Update Rollup 1) to Windows 2008 Exchange 2007 SP1 (+ Update Rollup 1). After the move of the CAS Role the OAB cannot be downloaded anymore. OAB is generated successfully but the download won't work. Everything is working fine on CAS - Autodiscovery, OWA, ... but OAB not. I checked all permissions on the file system and IIS 7.0. If I move CAS back to an Windows 2003 SP2 Server, the OAB download works fine. (Permissions have been compared between Windows 2003 and Windows 2008 IIS and file system) The only change in Windows 2008 --> IIS 7.0 with Kernel mode authentication (disable this feature on OAB virtual site does not solve the problem. OAB download should use "integrated authentication" but Outlook always asks for credentials (like Basic authentication is activated) Has anyone seen the same issue? If so, is there any solution for that problem. Kind regards Leo