Well the owner would be a verified customer if they match their email to the license email this explains the process
http://www.photopost.com/forum/before-you-buy/announcements.html
Okay lets try and rule out if permissions are correct that Imagemagick is broken
Try and go to admin global options and set your image processor to gd2 and upload the same file. If it uploads then the problem is with the servers imagemagick install.