The permissions are all ok, basically everyone has full control on the uploads and data directory. I have PhotoPost Pro 4.0.1 working on another Windows IIS 6 server I have, without any problems and even used this as a basic comparison for permissions and such. The only difference between these two boxes is the version of PhotoPost Pro and ImageMagick (the other box is using the version supplied from your site).
Anyhoo, I went with GD2 and it works without a hitch, tho I would still prefer to use ImageMagick, it just does not want to go for some darn reason. Gotta love IIS ;-)