The first thing to check is whether the client computer is using the latest Automatic Update client version.
The current version of the Windows Update Agent (the WSUS client component in AU) is determined by the version of the WUAUENG.DLL, located in %systemroot% \system32 folder. If the version of WUAUENG.DLL is 5.4.3790.1000 or greater, the WSUS client (or WUA) is installed. A version less than 5.4.3790.1000 indicates that SUS or earlier AU version 1.0 is installed.
If you have an earlier version of the AU client, it must be updated in order to work with WSUS. Computers running Windows XP with Service Pack 2 (SP2) already have the WSUS client installed.
The AU client, when contacting the WSUS server, will automatically update itself to the latest WSUS version if the self-update files are properly setup on the server. When connected to Windows Update or Microsoft Update, the AU client will also be able to self-update if it is not running the latest version. In addition, the AU client can also be updated by using a signed stand-alone, installation package that is available from Microsoft.
For further instructions on how to detect the need for, and or download the standalone latest release version of WUA, see the Updating the Windows Update Agent section of the Windows Update Agent API portion of the WSUS SDK at: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/wus/wus/portal.asp
On the left navigation, from Windows Server Update Services -> Windows Update Agent API -> Using the Windows Update Agent API -> Updating the Windows Update Agent.
Imaged clients with a duplicate client ID will only appear once in the WSUS Admin Console. Each AU client must have a unique id which is created for each individual install. When imaging systems it is recommended always to use SysPrep. The WSUS admin console will only display one client for each unique ID. If you have multiple clients created from one image which are sharing the same ID, only one will appear in the WSUS admin console. All clients will check in and download updates, but only one will appear and display status in the WSUS admin console. In cases where clients are not checking in, and they were created from images without running SysPrep, the following steps will reset the existing duplicative client IDs.
a. Run regedit and go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate
b. Delete the PingID, SUSClientID and the AccountDomainSID values
c. Stop and start the Wuauserv Service
d. From the command prompt run: wuauclt /resetauthorization /detectnow
From the command line, once you are sure the AU client is properly configured and not disabled, you could run a batch file (which might look something like this sample) and get the same results:
rem Fixes problem with client machines not showing up on the server due to imaging method
reg delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate /v AccountDomainSid /f
reg delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate /v PingID /f
reg delete HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate /v SusClientId /f
@echo Triggering detection after resetting WSUS client identity
net stop wuauserv
net start wuauserv
wuauclt /resetauthorization /detectnow