A while ago, I installed IIS7 on a client's production Windows Server 2008 machine, simply for testing out an application. After having done my testing I kept the server clean and tidy by removing the application and the IIS role from the server, and all seemed fine.
That is, until I came to install WSUS 3 on the server, today. On attempting to re-install the IIS7 role again - a pre-requisite for WSUS to function - Server Manager continually errored with an 80070643 error, giving very little information over and above that Error ID. After searching on the Internet, it turned out that Windows Process Activation Service (WPAS), which was installed when I initially installed IIS7, was causing the failure.
So, in future, if you have this issue, check to see whether the Windows Process Activation Service is installed. It is a Feature, and therefore visible in 'Features', in the Server Manager console. If it is indeed installed on the server, use the 'Remove Features' wizard to remove it, reboot the server, and then re-install IIS7, and you should be good to go.
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