Communicator 2007 R2 requires Microsoft XML Core Services 6.0 (MSXML6), which is an optional update through Microsoft Update or Windows Update. If MSXML6 is not installed on the computer, Communicator installation fails.

During an attended installation, the user will see an error message that provides a link to the MSXML6 download page. However, during an unattended installation, users will not see this error message and installation will fail. If you plan to deploy Communicator by using an automated method, ensure that MSXML6 is also installed on the client computers.

For more information about MSXML6, see Microsoft Knowledge Base article 934268, “Description of Microsoft Core XML Services 6.0 Service Pack 1,” at http://go.microsoft.com/fwlink/?linkid=147167 .

The Microsoft Core XML Services 6.0 Service Pack 1 download is available at http://go.microsoft.com/fwlink/?Linkid=144674 .