I fought with this one for nearly 8 hours today, attempting to install SSMS from SQL 2012.  This requires that the .Net Framework 3.5 and 2.0 be activated in Windows Features.  Sure, there’s a checkbox that you “should” be able to check and everything works fine.  Well, not for me.  I check it, click OK, it tells me it needs to download files from Windows Update, I say OK, and it throws this error.

Basic troubleshooting courtesy of Google says to make sure Windows Firewall is not blocking the connection, which in my case it wasn’t.  Next, make sure you can get to Windows Update in general, which I could.  Finally, it said to contact your IT administration…..which doesn’t help me because I *am* IT Administration (seriously?)

The solution (at least for me)?  Elevated Command Line!  Earlier I had to also activate my copy of Windows 8 Enterprise via command line thanks to a similar error.  I found this solution in an MS Support article, but here’s the general idea:

• Run gpedit.msc, and look in Computer Configuration > Administrative Templates > System.
• Locate the “Specify settings for optional component installation and component repair ” and open it up.
• Select “Enabled” at the top, and at the bottom, check the box next to “Contact Windows Update directly to download repair content instead of Windows Server Update Services (WSUS)“.
• Click Apply, then OK.
• Then run gpupdate /force at command line.

Next, make sure your Windows 8 install media is loaded in your CD/DVD drive, flash drive, wherever, open an elevated command line and type the following:

Dism /online /enable-feature /featurename:NetFx3 /All /Source:<drive>:sourcessxs /LimitAccess

Where <drive> is the drive letter of your Windows 8 media.  It took a few minutes, but worked like a champ!  Now the .Net Framework 3.5 feature was enabled without any errors.

Hope this helps!