I'm using Content Access to restrict Guests from seeing some content which is working fine, but is there no possibility to show a "access denied" message with this module?

I still can visit the denied url and get the heading but no content. Not that useful at all.

Comments

Create a basic page with your access denied stuff on it.
Then go to admin/config/system/site-information and enter the page title or node ID in the "Default 403" field.

That is not working as "Content Access" is not directing to a 403 page but only hiding the content.

A simpler module is Private which effectively hides nodes marked private and all links/menu items etc to them. Access to private content is set up in permissions. I use this module on my family history site where all content relating to persons living is marked private.
http://sandesancestry.net

checked this one out. But it is to simple. I have to block whole content types.

Ah, my fault. Content Access is working fine. My problem was that views showing blocked content are still working (and only showing the title).
I blocked the views and now everything is working as desired.