I recently ran into an issue on Server 2012 R2 with installing .net. I could not install the feature regardless of whether or not a source was sacrificed.

I attempted to redirect the GUI wizard to install sources on DVD, but that failed.

The command line: dism.exe /online /enable-feature /featurename:NetFX3 /all /Source:D:\sources\sxs Also failed.

I finally stumbled upon a forum where a user had success by removing these two Windows Updates: KB2966826 and KB2966828 and then attempting to run the command line install again.

This worked for me very well, and i wanted to make sure this was shared, as i had been banging my head against a wall for a few hours with this one.