From what I know, Paint.net 4.0 requires Windows 7 SP1 or newer, but not the older versions. I would recommend downloading an older version like 3.5.6 like I did until I can figure out the issue. I am indeed running on Windows 7 Ultimate SP1 (Or at least that's what it said on the box when I bought it) and came across this issue myself when I was trying to make a Minecraft resource pack. You may have to get it from an alternate site though, because for me I couldn't get 3.5.6 from getpaint.net, so yeah.
Also, if I just broke a forum rule by mentioning alternate sites, I apologize and plz have mercy on me admins.
