If you have been using the windows 8 developer preview you will encounter this window every time you try to run an app, is annoying. If you Accept the changes, you’ll be connected to Windows update and required files will be downloaded. But this process continues and never completes. If you cancel, no changes will be made and the app simply will not run.
To fix this permanently:
1. Open Control Panel > Programs > Programs and Features > Click Turn Windows features on or Off
2. Select .NET Framework 3.5.1 feature and click Ok, Windows downloads required files connecting to Windows Update
3. After downloading is compete, you will see “Windows Successfully completed the request changes” message.
That’s it from now on you can run any windows app without any problem.