I had this working since a long time and for some reason it seems it stopped working and I am not sure when nor how. I am using Seaside 126.96.36.199 on GemStone 3.3.3. The scenario I am describing is an error (DNU) raised at RENDERING time caused from a normal request (not AJAX).
On the server side, I am generating the response to the error this way:
"In case of a rendering error, we render the wallbackComponent but we do not render it;s buttons as callbacks won't work at this point."
wallbackComponent shouldRenderButtons: false.
[ html render: wallbackComponent ]
do: [ :ex | html render: 'Error rendering error page: ' , ex printString ] ]) ]
On Chrome, when I analyze this, I see I do get the 500 error and I get the correct html in the response. See attached screenshots from Chrom Dev Tools. As you can see, I do get the HTML, I can even preview it, and the error is 500. yet.... that HTML is not renderer in my browser. I mean...the browser keeps showing the original page that triggered the rendering error. Previously (when this was working) the page would be replaced with the HTML of the response which shows a nice error report.
Any idea what may have changed or what could be going on?