Windows Update failed on my PC earlier this week with error 0x80072EFD.  It is a very generic error that just means that the Windows Update client did not receive a response from the Windows Update Web site.

Microsoft KB article #836941 explains the steps that normally resolve the error but it did not work for me. In my case it was caused the Proxy auto configuration configuration script I am using.

The PAC script works grand when browsing but Windows Update refuses to work. Temporarily disabling the PAC script and configuring a static proxy works.

The proxy script below is based on one I got from Michele. It has the following features:

• Disables ads in Live Messenger and Live mail by sending requests for the host rad.msn.com to a proxy that does not exist :-)
• Uses direct internet access from home
• Supports different proxy configurations for several clients (I have changed the real IPs and hosts)

// Configure it as file://c:/scripts/proxy.pac
function FindProxyForURL(url, host) 
{ 
   // Set if (true) to show debug messages
   if (false)
   {
      alert(url);
      alert(host);
      alert(myIpAddress());
   }
   if (host == "127.0.0.1" || host == "localhost")
   {
      return "DIRECT";
   }
   // Disable Live Messenger/Mail ads by pointing to proxy that does not exist
   if (host == "rad.msn.com")               
   {
      return "PROXY 127.0.0.1:55555";
   }
   // Home Network
   if (isInNet(myIpAddress(), "192.168.10.0",  "255.255.255.0"))
   {
      return "DIRECT";
   }
   // Client 1. Direct access to local network and to Exchange server
   if (isInNet(myIpAddress(), "10.135.160.0",  "255.255.252.0"))
   {
      if ((isInNet(host, "10.135.0.0",  "255.255.0.0"))||(host == "owa.company.com"))
      {
         return "DIRECT";
      }
      else 
      {
         return "PROXY 10.135.160.4:8080";
      }
   }
  
   // Client 2
   if (isInNet(myIpAddress(), "10.10.0.0",  "255.0.0.0"))
   {
      if (isInNet(host, "10.10.0.0",  "255.255.0.0"))
      {
         return "DIRECT";
      }
      else
      {
         return "PROXY proxy.company.com:8080";  
      }
   }

   // N other clients here..
   
   // Anything else goes directly
   return "DIRECT";
}

A quick intro to the functions/variables used in the script:

• The host variable tells the script which site I am accessing
• myIpAddress() returns my ip address which changes according to my location
• I match my ip address against a subnet using isInNet() to know if I am at home, in the office or on site at a client
• The function returns the string “DIRECT“ if the host can be reached directly otherwise it returns “PROXY ip-or-host:port“

More info on how Windows Update works with proxies here:

• How the Windows Update client determines which proxy server to use to connect to the Windows Update Web site
• WinHTTP AutoProxy Support WinHTTP AutoProxy Support