Warning: Cannot modify header information - headers already

For both the Advanced poll and guestbook scripts...after executing them they work fine..but I receive this error.
:advanced poll:
Warning: Cannot modify header information - headers already sent by (output started at C:\JonoVision\index.php:9) in C:\JonoVision\poll\poll_cookie.php on line 21

I've searched the net for answers...but only find alot of people wondering...if anyone knows how I can make PHP happy...plz let me know.

Most of the time it is an cmod problem, try changing your setting of that directory.

i'm using iis on windows xp as my server. as far as I know all folders and files have access rights. It just doesn't seem to send out cookies because one person can vote over and over again every time the page reloads. I 'm just wonder why it might do that.

if you want to check it out for yourself...plz got to jonovision.com

i fixed that problem finally. i avoid gettting the message but i want to set it up so you can only vote once per poll.