Open a Powershell window. Run "Get-WindowsUpdateLog". That will put a WindowsUpdate.log file on the desktop. Review that and see if there are more errors.
Use Powershell to test the connection to your WSUS server.
Test-NetConnection YourWSUSserver -port 8530
PS C:\Users\Admin> get-help Test-NetConnection
NAME
Test-NetConnection
SYNOPSIS
Displays diagnostic information for a connection.
SYNTAX
Test-NetConnection [[-ComputerName] <String>] [-InformationLevel {Quiet | Detailed}] -Port <Int32> [<CommonParameters>]
In your WindowsUpdate.log you may see a reference to SimpleAuth.asmx. Something like http://YourWSUSserver:8530/SimpleAuthWebService/SimpleAuth.asmx
See if you can browse that.
Disclaimer: I no longer have access to a WSUS server. The above suggestions are from my "useful commands" notes.