How to diagnose why an update cannot be installed on Windows Server 2003

There is a Microsoft Support article (KB 836941) mentioned in this blog post which addresses this error number:

You may encounter temporary connection-related errors when you use Windows Update or Microsoft Update to install updates

In most cases, these messages are temporary or short-lived issues that are caused by very slight interruptions in communications between the computer that is being updated and the Windows update servers. These issues are generally self-healing. So, before you try the troubleshooting methods in this article, please exit the Windows Update site, wait 10 to 15 minutes, start Windows Update again, and then check for updates. You can also let Windows Automatic Update install the updates on its usual 24-hour cycle.

Note: These errors can occur even if no changes have been made to network settings.

Proposed resolutions:

Method A: Verify Internet connectivity

Make sure that you can successfully access other Web sites. If you can’t successfully access other Web sites, your Internet connection may not be working correctly, and you might want to contact your Internet service provider for help.

If you can successfully access other Web sites, continue with Method B.

Method B: Make sure that Windows Firewall is turned on, and temporarily disable third-party firewalls

Warning This workaround may make a computer or a network more vulnerable to attack by malicious users or by malicious software such as viruses. We do not recommend this workaround but are providing this information so that you can implement this workaround at your own discretion. Use this workaround at your own risk.

Method C: Temporarily disable third-party antivirus software

Method D: Disable software accelerator programs

Method E: Add the Windows Update Web site and the Microsoft Update Web site to the Trusted Sites list

Method F: Make sure that you have the latest Background Intelligent Transfer Service (BITS) update installed

Not sure about Windows 7, but with XP/Vista, you could run the following command to detect and download updates:

wuauclt /detectnow /reportnow

If you have issues getting it to work, check out the WSUS Wiki.

Otherwise if you have a specific update that you want, just download from the Microsoft website. If there's some problem preventing you from installing, that's the best way to find out, because the Windows Update logs are godawful to deal with.