Outlook 2003 running on Windows Server 2003 Service Pack 1 cannot connect to an Exchange 2003 server through ISA Server 2004 Standard Edition. Earlier versions of Outlook may also be affected. Windows Server 2003 SP1 makes significant changes to the Remote Procedure Call (RPC) service. Some of the changes may cause conflicts with ISA Servers RPC filter (rpcFltr.dll).
As a workaround, disable the RPC filter. Install this update to fix this issue without disabling the RPC filter. In Small Business Server (SBS) scenarios, this may commonly occur when Outlook is installed on a server running Terminal Services in application sharing mode. This version is the first release on CNET Download.com.