The request to add or remove feature on the specified server failed.
Installation of one or more roles, role services, or features failed. - The source files could not be downloaded.
Use the /source option to specify the location of the files that are required to restore the feature. The file location should be either the root directory of a mounted image or a component store that has the Windows Side-by-Side directory as an immediate subfolder.
From a administrative command prompt run the following:
dism.exe /online /enable-feature /featurename:NetFX3 /Source:d:\sources\sxs /LimitAccess /all
This will install .net 2.0 and 3.5.