WSUS - Clients not updating

If WSUS clients are not connecting to the WSUS server and giving errors
such as "WARNING: GetAuthorizationCookie failure, error = 0x800710DD" in
the WindowsUpdate.log file - you probably have a permissions issue on the
IIS WSUS site. To check that the permissions are set correctly use this:
http://technet.microsoft.com/en-us/library/cc708545%28WS.10%29.aspx

And to check the IIS Anonymous user password is in-sync with IIS follow
this:
http://blog.montopolis.com/2007/06/02/easily-resync-iis-anonymous-user-account/