I had some problems with my WSUS 3.0 SP2 server, so I had to repair/reinstall it. After reinstallation and configuration computers in my network refused to take updates and report to WSUS with error 800B0001.
After a quick research around internet, I find out about KB 2720211
I downloaded hotfix KB2720211, installed it, rebooted my WSUS 3.0 server, and after reboot everything was fine. Computers started to report and download updates from WSUS server.