If you receive Windows Update error 8024401b when checking for or installing updates, a problem prevented your proxy server from requesting your network credentials. A proxy server is a server that your computer uses to connect to the Internet or a network and, in this case, to download updates. Follow these steps to provide your credentials and install any available updates.
Open Windows Update by clicking the Start button , clicking All Programs, and then clicking Windows Update.
In the left pane, click Check for updates.
If prompted, provide your network credentials. If Windows doesn't prompt you to provide credentials and you see error code 8024401B instead, click Try again.
When prompted, provide the credentials that you use to access your network (for example, your user name and password). Windows will automatically continue the update process and notify you if you need to install updates.
If you continue to see this error, see this automatic troubleshooter
on the Microsoft Support website, or go to the Microsoft Answers
website for more assistance.
Help and Support search term: WindowsUpdate_8024401b