Hello all,
I am a long time user of Paint.NET though never registered here but it seems great so far! Great Program also, but anyway I was having a lot of trouble installing 3.5.11 on my new system so I will explain what worked for me and what I used.
1. Make sure the latest version of Microsoft Net Framework is installed.
2. If you have continued problem go to the link below and click on the green button that says "RUN NOW", a download will start, open the download and follow the directions. When the time comes to choose the program you are having trouble with choose "Paint.net 3.5.11" when is ask's did this fix your problem try to install paint.net 3.5.11 again and if it installs then click yes, simple as that!
**LINK http://support.microsoft.com/mats/Program_Install_and_Uninstall
Hope this helps!