SEMblog

Recently tried to install Net Framework 3.5 on to an existing server which had been in production for a few months. 

Constantly failing with an error about being unable to find the source files, even though it was using an ISO which was used to build this and many other servers in the past. 

Clutching at straws, discovered that the server had a Windows Update installed, released in September 2014 for Net Framework 3.5, even though it wasn't installed. Some research on the internet indicated that it was one of these three:

KB2966826

KB2966827

KB2966828

Removing the update then attempting the installation again was successful. 

Once Net Framework had been installed, I ran Windows Update to reinstall the update I removed, plus numerous others that were required for Net Framework.