I recently ran into this error while trying to activate the .net framework feature on Windows Server 2012 in azure:
The source files could not be found.
Use the “Source” option to specify the location of the files that are required to restore the feature. For more information on specifying a source location, see http://go.microsoft.com/fwlink/?LinkId=243077.
The fix is actually not to find the source but to actually remove the following KB articles:
Uninstall KB2966827 / 2966826 / 2966828