Why? (The Tough Answer with Gory Details): First of all thanks to Ken Schaefer of Adopenstatic.com for pointing out huge flaws and misleading information in this page as it was written before 1/10/2001. Its revision on 1/10 was prompted by Ken. He wrote an article on this too at http://www.adopenstatic.com/faq/headererror.asp...

That line will do away with all "headers are already sent" messages. It essentially tells the server don't write anything at all to browser until
a) response.end executes thus stopping the page dead in tracks and sending to browser
b) response.flush executes
c) 100% of the page is executed and it finishes all the ASP and HTML.
d) response.redirect is sent (provided no content or text has been sent with response.flush)

An ASP page must be sent to browser in a specific strict order: first the header, and then the content. The header could contain cookies (see http://www.learnasp.com/learn/cookies.asp), redirects, other headers inserted by the response.addheader command and other header information. If your page mixes content (any text) and mixes in header info this is not following the strict rules. If the browser writes any data that is page content, and then headers cannot be sent -- it is "too late" -- it can't change "horses in midstream" -- that is header info cannot come inside or after data. Buffering does not send the page content and headers in exact order they appear in script. Even if headers and content is mixed the header and content are sent in correct order when buffer is flushed (either by explicit response.flush or script completes).

The Recommend Book Sample Files provides you with several files that when created, prepare you for applying several powerful content management tools and session examples in the following pages. The features detailed will include:

• Include files that implement pages headers, footers
• sessions and application variables to track users accessing these pages
• the content linker component all come together in this example.

Here is the code for bookheader.asp