WSUS 3.0 - Computers Not Showing Up (no duplicate ID's)

I am not able to get my computers to populate the pc's list in the Update Services. There is a domain that I have with 300 machines and they are getting their update information via Group Policy and WSUS installed or setup on a Windows SErver 2003 box. All of these machines are not cloned and they all have different SID's. I have checked that the computer's are getting the policy correctly by browsing to HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate and seeing that the server name is in the list for the 2 entries: WUServer and WUStatusServer, in the "http://servername" format. I am able to ping/rdp the server from any machine in the network. Can anyone help me out.

Try the below steps after you have done all the things as you have said:

1. First of all download and run the Client Diagnostic Tool on one of the computers and then post the results.
2. After that, restart the PC.
3. Now after the computer boots, run this command 'wuauclt /resetauthorization /detectnow' and wait for half an hour lets say.
4. Now you have to post the resulting entries from the WindowsUpdate.log, starting from the time of the restart.

After getting all this results we will be able to identify the cause of your failures, and possibly identify a short list of solutions.

Even I am facing this same problem. Most of the computers that we have are not showing up in the WSUS panel. A good part of them were solved by deleting the AccountDomainSid, PingID, and SusClientId keys and reauthorizing but there are also many that are not solved by this. They are able to see the WSUS server and also see that there are no updates, but they simply cannot show up in WSUS.

It could be a problem due to the duplicate WSUS client IDs in the registry of the machines that are not showing up on the WSUS server. You will need to delete the entry called SusClientid in the following keys - HKEY_LOCAL_MACHINE>SOFTWARE>Microsoft>Windows>CurrentVersion>WindowsUpdate. After that try to restart the computer and then open a command prompt and type: wuauclt /resetauthorization /detectnow then press enter.