There are some older applications that require earlier versions of .NET than the version included and enabled by default on Windows 8 and Windows 8.1. Normally you can enable the .NET Framework 3.5 (which includes .NET 2.0 and .NET 3.0) as a Windows Feature. (Control Panel, Programs and Features, Turn Windows Features on or off.) But in some environments, especially those using SBS and WSUS, you may get an error message:
0x800f0906: “Windows couldn't connect to the Internet to download necessary files. Make sure that you're connected to the Internet, and click Retry to try again.”
This, of course, is totally bogus because the computer IS connected to the Internet, but save yourself some grief and do it from the command line in the first place. The files you need are part of the DVD (or USB stick or whatever) that you used to install Windows. Just insert that media and from an elevated command or PowerShell prompt type:
PSH> DISM /Online /Enable-Feature /FeatureName:NetFx3 /All /LimitAccess /Source:E:\Sources\SxS
Deployment Image Servicing and Management tool
Image Version: 6.3.9600.16384
The operation completed successfully.
Where the E: drive in E:\Sources\SxS is replaced by the drive letter of the DVD, USB or other media source or your Windows distribution media. Or, the pure PowerShell way:
PSH> Enable-WindowsOptionalFeature -Online -FeatureName "NetFx3" -All -LimitAccess -Source "E:\Sources\SxS"
Now, whatever application it is that needs this older version of the .NET Framework will be happy. (Zune 4.8, in my case.)
Updated: 13 November 2013: Added PSH equivalent.
: 2 June, 2014: Fixed curly quotes
: 13 October, 2014: Confirmed, the same command works in Windows 10 Preview