Windows Search 4.0 has been available on WU for a few weeks now, Microsoft has confirmed that the upgrade it’s pushing via Windows Update for the search infrastructure in the Windows operating systems has problems integrating with some copies of Windows XP and Windows Server 2003. However, according to a member of the Microsoft Update team, the fault lies with neither Windows Search 4.0, nor with XP or Windows Server 2003. Still, there are scenarios when the search update served via WU will fail to integrate in the Windows client and server platforms mentioned above, producing the 0x643 error code.
“We've done some investigation and found out that the installation failure in this case may actually be caused by the computer configuration, which in most cases can be easily changed to allow for successful installation and functionality of Windows Search 4.0. In this case, when WS4.0 runs under Windows Server 2003 or Windows XP, it requires Terminal Services to be running. By default, Terminal Services are set to start automatically in Windows XP and Windows Server 2003; however, system administrator or third-party software may have chosen to disable them. In order to enable installation and subsequent functionality of Windows Search 4.0 on your machine, you need to have Terminal Services running first.” the MU team representative added.