I had this problem after updating win 8 to 8.1 and installing loads of programs of which one suddenly wanted to install Net3.5 first before it would install. Trying to do this by various means always led to the same win error message that I could not download the necessary updates.

After reading loads of threads and forums on this subject, and trying various ways of solving the problem including the ones that MS themselves have on their website under that error message, I still could not download Net3.5.

Then I found a couple of posts somewhere that said you had to do it before updating to Win 8.1, and then another that said 'No, all you have to do is uninstall win updates KB 2966826 and KB 2966828'. I thought it worth a try and lo and behold IT WORKED!! All I had to do then is to go to the 'Turn windows features on and off' in the win update dialogs, check the top box for Net 3.5 and it installed. It didn't before removing those two security updates.

Then I ran Win update to reinstall those two now-missing updates.

It would be nice if MS modified those two updates to stop this problem, but at least I had a simple solution. Thanks to the person (not remembered by me) who posted that solution somewhere.

Bob Frost