Problem: MS Office Communicator 2005 fails to install

In my current company, I’m forced to use IM which is MS Office Communicator 2005. Accidentally (or perhaps my tortured subconsciousness told me do so;), I uninstalled this thing. Unfortunately, re-installation of this application wasn’t so easy as it seemed to be. When I ran installer it exited saying that Communicator could not be installed. That was really strange. After a couple of hours, I’ve finally realized that configuration of my workstation doesn’t really differ from the configuration of a typical WinXP machine, so the problem may be in some service pack or some security update. And that was it. A little creature named “Security Update KB974571” was the reason causing the failure (it was enough to uninstall it and reboot the computer). I wasted about 4 hours of my life which could be spent on coding.