Error- Cannot modify header information - headers already sent

[eluser]bleu[/eluser]
I am getting this error when I use this

Code:

header("Location: /");

to redirect to home page.I believe there is a javascript alert which come before this is called, that gives the below error, I cannot remove the alert so is there nay other way I can go about redirecting without giving me the below error ?

Code:

A PHP Error was encountered

Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at /home/dsdsd/application/core/MY_Controller.php:dsdsds)