hopefully we'll get a FAQ up soon about the various discussion board programs and their relative merits (and relative use of system resources).
if you continue to have problems, you should contact support as they can actually go look at your permissions and see what's going on. you might also check in your error logs, although most likely the message will be something fairly non-specific.
first of all, make sure your plan supports custom CGI. if you're on a crazy domain insane plan, you'd need to upgrade before using a script like this (or use a PHP forum).
problems with CGI scripts are almost related to file permissions; if that's the case, you will want to make sure that the file permissions on executable scripts (ie the script you're trying to run) are set to 0755. from the command line, just do:
chmod 0755 filename
the way to do this in various FTP clients differs.
if you are using ssh or telnet to connect, try running the script from the command line. first try:
from the directory it's in. do either of these command spit out errors?
have you opened the file on your home computer at all? windows and macintosh computers sometimes insert carriage returns that UNIX and linux systems don't like; this will break the script as well.
make sure that you're uploading the files in ascii or autodetect mode if you're using FTP; uploading them in binary mode will mess things up.
in any event, if you can't fix the problem easily, i'd recommend writing support. they handle stuff like this all the time, and may be able to help you out if the problem can be fixed easily.