The first output of a CGI script should be a header, such as:

Content-type: text/html
[download]

The first blank line output signifies the end of the header. If the script never output a blank line, for whatever reason, you get that error.

Look up the CGI::Carp docs for some tips on diagnosing CGI scripts. Make sure your script doesn't use DOS line endings on a Unix server, especially at the end of the first shebang line. Make sure you have set the permissions for any uid on the server to execute the script. Check your server's logfiles.

--
[ e d @ h a l l e y . c c ]