Why is my computer not updating via Windows Update?
Solution 1:
This could be that WSUS needs to be updated to manage Windows 8 clients. This was an issue with Windows 7 clients and WSUS and an update fixed the issue. A. Not sure that there is an update to support Windows 8 at this point but one MS forum indicates that KB2734608 addreses the issue. Later it indicates that fix is not available but points to other updates. WSUS Discussion
Solution 2:
You may need to install KB2720211 on the WSUS server. Source: http://social.technet.microsoft.com/Forums/en-US/winserverwsus/thread/8ebfbc1e-06e5-43c5-a540-1ca37c6ffff9/