"Microsoft .NET Framework 3.5 installation has failed.
SQL Server 2008 Setup requires .NET Framework 3.5 to be installed."
The solution I found deep in a thread in MSDN. The point of this blog is to make things like this easier to find on the web, so here goes.
- Copy your media to a folder on the server. You need to update a file in there.
- Download a fresh copy of dotNetFx35setup.exe from Microsoft
- Copy the new file and overwrite the old in this location in the media: ..\x64\redist\DotNetFrameworks\