I apologise if I haven't provided the correct information, I was doing my best to provide information what I thought to be relevant. Everybody thinks about how to solve problems a little differently.

I in fact did analyse the HTTP traffic (with Fiddler) even before I created this thread but nothing jumped out at me. I may be repeating myself here as some of the questions I have already answered but here goes... No there is nothing wrong with the generated HTML. Yes the browser attempts to load the image. What is returned - if you mean in the browser, a broken image icon until the page is refreshed (if you meant something else, please specify). Content-type is returned as text/html before the refresh but after, it is img/png. If I understand your question about the HTTP stream correctly, output from Firebug indicates there is some kind of timing problem of when the HTML is displayed and the image generation is completed. Additionally, when the image doesn't generate and I view the text output it reports a 502 error: "502 - Web server received an invalid response while acting as a gateway or proxy server" which I guess, suggests a problem with the CGI code.