redirect('home', 'refresh'); SOMETIMES IT DO, AND SOMETIMES IT DON'T

[eluser]cobolCowboy[/eluser]

A PHP Error was encountered
Severity: Warning
Message: Cannot modify header information - headers already sent by (output started at C:\wamp\www\app\controllers\login.php:1)
Filename: libraries/Session.php
Line Number: 676

I'm tearing my hair out!!
There is no whitespace anywhere, there are not ending PHP tags in any file. I've tried the function

Code:

public function _output($output)
{
    echo $output;
}

and even commented the echo, at which point it continued to display the error and nothing else.
I've considered perhaps a fundamental flaw in my approach, but to be honest its no different from any other. I don't know what else to do.

[eluser]TheFuzzy0ne[/eluser]
That looks to me like you have a whitespace before the opening PHP tag in ./app/controllers/login.php