Windows 8.1 comes with Windows 4.5 .Net framework, but not 3.5 .Net framework.  In order to install it, you go to Control Panel /  Programs / Uninstall a program / Turn Windows features on or off

The top option will be .NET Framework 3.5 (includes .NET 2.0 and 3.0)


This works great, unless you are using an alternate location for windows updates, which is most large networks.  If that is the case, you can load it directly from the source media.  You can put the Windows 8.1 media in your DVD drive or mount the ISO file locally.


Run a command prompt as an administrator.  Replace D: in the command below with the drive letter of your Windows 8.1 media.
DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:D:\sources\sxs