If you have a computer that was imaged without using sysprep first, or just a computer that is having problems registering itself with WSUS, this fix might help:
net stop wuauserv
cd %systemroot%\SoftwareDistribution
ren Download Download.old
net start wuauserv
net stop bits
net start bits
net stop cryptsvc
cd %systemroot%\system32
ren catroot2 catroot2old
net start cryptsvc
Copy and paste into a notepad document and save it as a ".bat" file. Name it whatever you want and run it on the affected computer