Solving "WSUS administration console was unable to connect to the WSUS Server via the remote API" error

Today, I've got below when I try to connect my WSUS Server via WSUS Console.

Below logs are display in Event Logs too.

The WSUS administration console was unable to connect to the WSUS Server via the remote API. 

Verify that the Update Services service, IIS and SQL are running on the server. If the problem persists, try restarting IIS, SQL, and the Update Services Service.
The WSUS administration console was unable to connect to the WSUS Server via the remote API.
Verify that the Update Services service, IIS and SQL are running on the server. If the problem persists, try restarting IIS, SQL, and the Update Services Service.
System.Net.Sockets.SocketException -- No connection could be made because the target machine actively refused it 172.16.99.98:80
Source
System
Stack Trace:
   at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddress socketAddress)
   at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Int32 timeout, Exception& exception)
** this exception was nested inside of the following exception **

System.Net.WebException -- Unable to connect to the remote server
Source
Microsoft.UpdateServices.Administration
Stack Trace:
   at Microsoft.UpdateServices.Administration.AdminProxy.CreateUpdateServer(Object[] args)
   at Microsoft.UpdateServices.Administration.AdminProxy.GetUpdateServer(String serverName, Boolean useSecureConnection, Int32 portNumber)
   at Microsoft.UpdateServices.UI.AdminApiAccess.AdminApiTools.GetUpdateServer(String serverName, Boolean useSecureConnection, Int32 portNumber)
   at Microsoft.UpdateServices.UI.SnapIn.Scope.ServerSummaryScopeNode.GetUpdateServer(PersistedServerSettings settings)
   at Microsoft.UpdateServices.UI.SnapIn.Scope.ServerSummaryScopeNode.ConnectToServer()
   at Microsoft.UpdateServices.UI.SnapIn.Scope.ServerSummaryScopeNode.ConnectToServerAndPopulateNode(Boolean connectingServerToConsole)
   at Microsoft.UpdateServices.UI.SnapIn.Scope.ServerSummaryScopeNode.OnExpandFromLoad(SyncStatus status)

Time to investigate for why?

As mentioned in Log, I restarted Update Services service, IIS and SQL Service. Then try to connect again and still the same error pop out.

Second, I try to test the port 80 of WSUS Server whether open or not from other Serverby using  Telnet WSUS Server Name/IP 80 .
Port 80 is not opened. Then pretty sure Default Web Site Service of WSUS has been stopped for some reason.

Just go to IIS Manager and Start the Default Web Site. After that try again connect the WSUS Console and it's working then.

Actually, the error is come out because of me. Last day, I was tested WhatsUp Gold Network Monitoring Application by installing and that use IIS and SQL. I uninstall it after tested and didn't check WSUS that time.

The root cause is uninstalling WhatsUp Gold without checking properly.

So if you are having such kind of error, do not forget to check above steps what I did to bring up WSUS again. :P

My Server is Windows Server 2008 R2 SP2 and WSUS is 3.0 SP2.

May you all be happy.
(Be knowledgeable, pass it on then)