This is useful when the Windows Update icon disappears when you click it. Typically, this means that the Windows Update client is corrupt. When you run wuauclt /ShowWU on these machines, it will bring up the Windows Update dialog box above, but it will show some type of error indicating that it could not download updates. Installing the current Windows Update client will fix this.
You can download the latest Windows Update client (7.2.6001.788) from these locations: