Yeh, if the cgi scripts can't see the variable files (or member files) then it'll error out.
You could try putting a php script in your web root named phpinfo.php containing:
And accessing it with your web browser, then looking for the "SCRIPT_FILENAME " variable, this would at least tell you what your non-cgi path would be (and from that you would probably be able to piece together your cgi-bin directory)
An example would be:
SCRIPT_FILENAME /var/www/public_html/phpinfo.php
So we can see that /var/www/public_html contains the file I uploaded to my /public_html folder, so the noncgi path if I put a ubb directory in my public_html folder would be /var/www/public_html/ubb and if my cgi bin was a folder named "cgi-bin" in the directory where my public_html folder was then it'd be /var/www/cgi-bin/ (likewise the same with say a members folder)
