I would assume that it is something about an incorrect path. What does it say in the webserver logs, e.g. /var/log/httpd/access.log or .../error.log
Can you write the CGI to return information about what it is trying to do to the screen? If it's Perl CGI, something like printf "Here I am\n" ; should give you a message. You can then experiment with what it shows you so you can see what you are really trying to call, and if it exists. Remember that your CGI script will be running as the webserver, not yourself.
As another thought, how will you stop someone just connecting and running this over & over again, clogging up your server?