Just installed both captcha and guestbook plugins and I am having "no direct access allowed" error message.
Before going deeper, could anybody tell me if they are compatible with CB121, or not?
And what about enter that information (version compatibility) in plugin downloads page?
I'll bet you're using plugin's that are not for J1.5 native, yet you are not using legacy mode. Either enable the legacy mode joomla system plugin or uninstall the CB plugins that do not support native.