WSUS doesn't synchronize first time

[leoatul]

Hi!
I have installed WSUS on my Windows Server 2003 computer which is also the primary domain controller. Before installing WSUS, I installed IIS 6.0 with default configuration.

I am not using any proxy server on my network.

WSUS installation went fine, but if I try to synchronize my server, it gives me the error below.
There was an error communicating with the upstream server. Please check your update source and proxy server settings on the Synchronization Options page

if I click "Details" it shows

WebException: The underlying connection was closed: Unable to connect to the remote server.
at System.Net.HttpWebRequest.CheckFinalStatus()
at System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult)
at System.Net.HttpWebRequest.GetRequestStream()
at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters)
at Microsoft.UpdateServices.ServerSyncWebServices.ServerSync.ServerSyncProxy.GetAuthConfig()
at Microsoft.UpdateServices.ServerSync.ServerSyncLib.InternetGetServerAuthConfig(ServerSyncProxy proxy, WebServiceCommunicationHelper webServiceHelper)
at Microsoft.UpdateServices.ServerSync.ServerSyncLib.Authenticate(AuthorizationManager authorizationManager, Boolean checkExpiration, ServerSyncProxy proxy, Cookie cookie, WebServiceCommunicationHelper webServiceHelper)
at Microsoft.UpdateServices.ServerSync.CatalogSyncAgentCore.InternalGetConfig()
at Microsoft.UpdateServices.ServerSync.CatalogSyncAgentCore.CatalogSyncThreadProcessReal(Boolean allowRedirect)

I have tried uninstalling WSUS and installing again but all in vain. I would really appreciate if someone could tell me if there is some setting on IIS which I need to change to fix this error.

Thank you,
Atul