session Error

[eluser]Bigil Michael[/eluser]
while running the project as localhost[ in my local machine] it shows a warning like this

Code:

A PHP Error was encountered

Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at C:\xampp\htdocs\classic\system\libraries\Exceptions.php:164)

Filename: libraries/Session.php

Line Number: 662

in server it runs fine. no session warning.

i checked each and every pages of my code, is there any white space before <?php or after ?>
everything is fine.
my project will become live very soon. so i fear that is this code generate any session warning in server.
if it generate any problem my project will cancel...

so i am in big trouble can anyone help me????
thanks in advance..........