A little bit more info than this is genrally needed. Please enlighten us to how the CGI application misbehaved.

I get the message:

--Begin of message--
CGI ERROR
CGI application misbehaved by not returning a complete set of headers. The headers that it did return are:
--End of message--

In three situations:

1. A random error that corresponds to a bug in PHP 4.03pl1. The message does not appear after refreshing the page. The condition to reproduce the error has not been identified, but is more likely to happen when using header("Location: http://mysite.com/path/to/my/file.php");. It happens even if you check that no output (such as carriage returns or spaces) has been sent before the header instruction.

2. While setting headers after headers have been already sent. Functions like setcookie, header and session_start can set header information. If headers have been already automatically sent by some output, the error is likely to occur.

3. When requesting an URL with a file or directory that doesn't exist. THIS IS NOT A BUG. It only happens if you have not checked the checkbox in:
Internet Information Services >> Web Site Properties >>
Home Directory >> Application Configuration >> Add/Edit Application Extension Mapping >> Check that file exists.

Can this be reproduced with PHP 4.1.0?

No feedback. Closing.