during your installation you come to a page where it asks for certain paths to certain applications. php, mogrify, composite,convert. you have not provided the correct path for the script to be able to run. if you can login to a shell account you can find the paths to these by typing the commands:
which mogrify
which composite
which php
which convert

now where you are supposed to change these once you have ran through the setup is something i dont know, but would seem to me this would be in see more a config file. but the bottom line here is that you didnt provide the necessary information during the installation, nothing wrong with the script.

later,
DosDawg