Event ID: 4999 is frequently generated in a mixed Exchange Server 2007 and Exchange Server 2003 environment


In a mixed Microsoft Exchange Server 2007 and Microsoft Exchange Server 2003 environment, an Exchange Server 2007 Client Access Server (CAS) server handles the proxy requests for Exchange Server 2003 servers. After you upgrade an Exchange Server 2007 CAS server to Exchange Server 2007 Service Pack (SP2), you may frequently receive the following event in the Application log on the Exchange Server 2007 CAS server:

This problem occurs when the following condition is true:
  • The Exchange Server 2007 CAS server is located in a different site from the Exchange Server 2003 servers.
Note Although there is no other obvious problem, Event ID: 4999 may alert users about the W3Wp.exe process that crashes.


This issue occurs because certain operations on the Exchange Server 2007 server check the site related attribute from Exchange Server 2003 servers. However, this attribute is not provided and Exchange Server 2007 does not handle the null response well.


To resolve this problem, install the following update rollup:
2407025 Description of Update Rollup 2 for Exchange Server 2007 Service Pack 3


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.