[Zope] standard_error_message behavior

Why is standard_error_message called only sometimes? I've overridden standard_error_message on my site to print "Mysterious Error has Occurrred" and email me. It works when I call one of my DTML methods that requires parameters without parameters, i.e. http://www.centralchurchyouth.org:8100/search? invokes standard_error_message OK because the keywords parameter is not specified However, on a simple notFoundError, standard_error_message isn't invoked, i.e. http;//www.centralchurchyouth.org:8100/page_that_does_not_exist shows a standard Zope error screen. Is this supposed to be this way? If not, how can I make my standard_error_message be used in all situations? -- Stephen Pitts smpitts@midsouth.rr.com