Problems with Guestbook v.1.51

Whenever I try to submit a test entry to my guestbook I get this message:

Cannot create ID file guest_id.txt in http://www.maybe-fiction.net/alteredboy/cgi-bin/guest. Please check your base directory.

Everything else seems to work just fine, and I've tried chmod-ing guest_id.txt to 777 and 755 but to no avail. Any suggestions?

Lol
a base directory is not an URL!!!
it's the path from the server root.

Could you give me an example of what the base directory path should look like?

e.g. "/home/you/public_html/alteredboy/cgi-bin";