if you have problem like me
which is WSUS server on OS windows server 2008r2 and have client with OS windows
server 2012R2 that doesn’t connect to the WSUS with error code 800B001
You need to install below KB , and then restart the server
After server going up and then test the update on client.
Hope it will solved your problem just like me🙂
I found this workaround on this site :