about guestbook v1.5

Hi there!
I tried to run the script of guestbook v1.5 and when I entered all the content and pressed the submit botton, it prompted me with the following error message:

Guestbook - Error
Cannot create ID file guest_id.txt in /var/www/book. Please check your base directory.

The system showed me part of the environment variables as follows:
HTTP_REFERER http://raymondip.no-ip.com:8080/book/addentry.html
REQUEST_URI /cgi-bin/guestbook.pl
SCRIPT_FILENAME /var/www/cgi-bin/guestbook.pl
SCRIPT_NAME /cgi-bin/guestbook.pl

I have put all files (chmod 644 in ascii) in directory "/book" in the directory of "/var/www/book" (chmod 644) and configured the following alias in my httpd.conf (Linux 9.0)
Alias /book "/var/www/book"

What did I miss?

Cheers.

I don't use this version of the guestbook, but I'd guess that you need to chmod the guest_id.txt to 777 .