Recently I was trying to install Ncover in Windows Server 2008. Even though I had installed .Net framework 4.0 Ncover setup threw an error saying that "you need to have .Net 3.5 or above to install NCover".I had re installed .Net Framework 4.0 several times ad restarted the server but no effect.
Then I went to the server manger panel and I saw a section called feature summery. In add features section you can add .Net framework 3.5 features. After a restart everything worked fine.