I've change my standard_error_message method. But it's not enough. How can I change the page that my guests will see when they do a "Site Error" like Unauthorized, Debugging notice... ?

Hi! The errors that have to do with authorization are handled by ZPublisher. If you are not authorized, ZPublisher will not let you access anything, not even standard_error_message. That's why these error messages were hard-coded into ZPublisher at "HTTPResponse.py" in lib/python/ZPublisher, starting at line 496 You can change the HTML code there if you want to have a customized error. You might also put an HTML-based redirect into the HTML header and redirect it to some non-protected Zope error page. I have the feeling that this should change with some later version of Zope -- having hardcoded HTML error messages in the Python code is not THAT cool ... Joachim