403 error: not authorised to view this resource

[quodo]

I installed easybook 2.0 rc4 on Joomla 1.5.14 (will update to 1.5.15). The site uses PHP5.2.4.
Backend setting is changed to allow "everyone" to enter a guestbook message. The dutch language, which I'm using, installed just fine ;-)

When I enter a message and hit the submit button I get a 403 error: "403 - You are not authorised to view this resource.". When I'm logged in as an administrator there is no error.

The "Sign guestbookSign guestbook" link is also unavailable when I'm nog logged in.

Installing EasyCaptcha did not help. In the preferences I set 'use the captcha' to 'yes', but the captcha does not show.

All help is appreciated as I like what this Guestbook can do and how it looks so I'd like to use it :-).