i also am having this error 1603 issue to.I had it on here a couple days ago and deleted it do to some issues i thought i was having with a couple plugins.When i go to my programs file and look up paint.net folder the only thing it has in it is a folder called
staging>
PaintDotNet_523301559
PaintDotNet_1392516740
PaintDotNet_1608653602
PaintDotNet_1856176814
And the version im trying to download is 3.5.8
EDIT
ok i did a system restore to about 5 days back and i have my paint.net back,but im still having issues here