I had an issue where I had several computer that were downloading and updating from the WSUS server, but they were not reporting.  I could see the in WSUS the computers checking in, but the last report date was not changing.  To resolve the issue I performed the following steps on the PC

1.  Open a command prompt as administrator.
2. net stop wuauserv
3. Open regedit as administrator
4. Delete the following keys
   1. HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate \SusClientId
   2. HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\WindowsUpdate \SusClientIdValidation
5. Back in the command prompt – netstart wuauserv
6. wuauclt /resetauthorization /detectnow
7. Go into update settings and check for updates
8. Back in the command prompt – wuauclt /reportnow (This step is not necessary, but it should force the PC to report now instead of waiting 20 minutes)

After performing the above steps I check WSUS to make sure the PC is reporting.