Heater problem - can't find any white spaces

[eluser]überfuzz[/eluser]
I'm tinkering with a site that's quite old by now. It's based on codeigniter 1.7. Now I get this message:

A PHP Error was encountered

Severity: Warning

Message: Cannot modify header information - headers already sent by (output started at xxxxxx/application/config/config.php:1)

Filename: libraries/Session.php

Line Number: 662

When I google this topic everyone point towards possible white spaces in the referred file. But I can't find any in my config-file. I'm pretty sure this was honky dory when I did the site. Any suggestions on what I should search for errors..?

Cheers!