this can happen for a couple of reasons.
First thing I would check is the following security setting (it should be set as shown)...
This setting must be disabled as shown.
The second thing to check is a hostname alias for the WSUS Server. If the WSUS Server has an alias, you MUST use the actual name of the WSUS server, or you can recieve this 401 error. So, when registering the WSUS server, the name used for registration needs to jive with the primary hostname of the WSUS server.
The last thing to check is that the account being used (DomainName\alex) and the password in the credential are correct. IOW, the account is at least a WSUS Administrator on the WSUS server AND the password that was entered for the account was correctly entered.
If neither of these represent a viable workaround, please contact Customer Support and we will work directly with you.