Cannot post with JunkMark enabled

[Vilkku]

Script URL: http://users.abo.fi/wtornroo/incl/guestbook/gbook.php
Version of script: 1.6
Hosting company: Åbo Akademi (university)
URL of phpinfo.php: http://users.abo.fi/wtornroo/phpinfo.php
URL of session_test.php: Sessions disabled.
What terms did you try when SEARCHING for a solution: Forum search, readme search

Write your message below:
Right, I'm having a bit of a problem with my GBook installation. The problem is, when I post a message and JunkMark is enabled the message will not post, no message from GBook, just a blank page with the header visible. When I disable JunkMark in the settings, it works fine. I tried to increase the score required before it gets marked as spam up to 100, and it still won't work (but it won't ban my IP address either, which it should if the score goes over 100). It's a clean installation, I haven't used any previous versions.

These are the current settings (note that they might change at any given time if I'm playing around, but I will always try to revert to these when I'm done if I can't come up with a solution myself):
$settings['junkmark_use']=1;
$settings['junkmark_limit']=60;
$settings['junkmark_ban100']=1;
$settings['ignore_proxies']=0;

Note that the PHP installation does not have the required module for the CAPTCHA image to display properly, so I am already forced to use the plain text verification, which isn't very secure, so I hope I can get JunkMark running to prevent spam. Thanks!

[Klemen]

Hi,

Your PHP isntallation needs to have ZLib library enabled, when compiling PHP add '--with-zlib'
http://www.php.net/manual/en/zlib.setup.php