This question already has an answer here:
my site works well in localhost (everything works fine)
but when I upload it in web and try to redirect the page after updating the data it says -> Cannot modify header information
</div>
95% you are trying to set a cookie, mime-type or redirection (short: http header) after you have sent http body, i.e. content. Check if you you have anything including whitespaces outside the php delimeters.
If you use the header function you have to be careful... You can't send any header before the "header location".
ob_start('mypage');
<html>
// Your code ...
</html>
ob_end_flush();
What's the error ? (php.ini, active the errors)
Else you can use the ob_start() function !