Problem with header

[eluser]Sceok[/eluser]
Hello everyone,

I'm new to CodeIgniter and have read a lot about on the purpose of avoiding annoying you all.
But I have a problem I can't fix and the worst is that I'm almost sure that it comes from a small mistake but here's the thing :

I'm trying to create a script that would set some variables like $config[base_url]/$assign_to_config['base_url'], $config['index_page']/$assign_to_config['index_page'].
I include the script in my index.php where it is written to be the place for custom values then it gives values to cells of $assign_to_config.
When I try to log onto my website i get that error message :

A PHP Error was encountered

Severity: Warning

Message: Header may not contain more than a single header, new line detected

Filename: helpers/url_helper.php

Line Number: 542

If someone could please give me an hint it would be cool

Thanks for your help.

PS: Sorry for my bad english, it is not my mother tongue ^^'