I am getting the following error with windows update and cannot get the update to install. Security Update for Microsoft .NET Framework, Version 1.1 Service Pack 1 (KB886903) Installation date: 10/11/2007 3:10 AM Installation status: Failed Error details: Code 643

This KB may be able to help with your issue: http://support.microsoft.com/kb/923100/

I had the same problem. This was being caused by Bitdefender (My antivisrus software) stopping the update of the registry. When I tried again BitDefender gave me the option of allowing the update - this option was selected and the update applied successfully.

Ok, I have just managed tofix this error after many attempts. Here it is. First, I downloaded "windows install cleanup" tool. next goto "add remove programs" and manually remove .NET Framework, Version 1.1 Service Pack 1 If like me it appears not to work you need to run the Cleanup tool you just downloaded and remove the service pack. After this you need to manually download and Install the service pack direct from the microsoft website, use the following url http://www.microsoft.com/downloads/details.aspx?familyid=A8F5654F-088E-40B2-BBDB-A83353618B38&displaylang=en. After you have installed this you will need to restart your pc and then goto windows update and run it. Hope this works for you, it worked for me and I was really getting fed up with this error, I cant believe Microsoft have not put out a patch for this problem. Good hunting

thanks Paulit works. one thing to add.before installing the .net framework 1.1 service pack 1. you might want to install the .net framework 1.1 package first. or there is an error coming out when you try to install the service pack 1.

ola eu estava com mesmo problema eu retirei net framework 1.1 baixei atualizaçao e depois baixei o net framework 1.1 deu certo