As a troublesooting procedure, it may be necessary to re-install the Automatic Client software on a WSUS client system (i.e. Windows XP systems).
You can do this as follows:
1. Go to the Windows Command prompt (CMD.EXE).
2. From the CMD.EXE prompt. run the following command:
For Windows XP SP2
rundll32.exe setupapi,InstallHinfSection DefaultInstall 132 %systemroot%\inf\au.inf
For Windows XP RTM and SP1
rundll32.exe setupapi,InstallHinfSection AutoUpdate 132 %systemroot%\inf\au.inf
Running this command prompts you for the XP installation CD. Alternately, use Browse button and navigate to C:\Winnt\Servicepackfiles\I386 where wuapi.dll and other files related to Automatic Update Client can be found. Afterruning this command, you must restart your computer.
Once restarted, you can open the Services control panel applet and check to ensure the Automatic Update Service is installed.