header error

[Anonymous]

i get the following error
Warning: Cannot modify header information - headers already sent by (output started at F:\portsaidmall\Register.php:2) in F:\portsaidmall\Register.php on line 10


here is my code:

<?php
//i check to make sure the user clicked the agee to terms check box
//on the previous page
if(!isset($_POST['box1]))
{
header("location: NoTerms.html");
}

?>

i m not sure why i get this error, i have used header("location:") before, and sometimes i get the error, and sometimes i don't get the error, the whole thing is very confusing...can someone please clear this error message up for me

 

[Anonymous]

Headers cannot be sent after normal text has been sent to the browser.

Possibly you have some newlines or blanks in this script or in scripts that are included. Those will be sent to the browser as normal text and would cause this error.

Coditor