Your issue has nothing to do with our software yet software outside of ours. Photopost needs one of these image processors correctly installed to work. We have no control over the server end of things on your server or your installs of ImageMagick and GD. We have extensive documentation on how to install them. http://www.photopost.com/howtoinstall-php.html http://www.boutell.com/gd/manual2.0.1.html
If your getting permission errors on ImageMagick and you have all permissions set right within our program then I would lean towards what I have already stated. The required libraries have not been found for ImageMagick to process those images. This is very common for people trying to compile ImageMagick on a FreeBSD system.
You need to do one of two things.
Install ImageMagick again with all the required libraries
Use GD to process your images.