After adding a title to my index.php page I started to get this error.

Warning: Cannot modify header information - headers already sent by (output started at /Library/WebServer/Documents/ Websites/forestgumpsays/index.php:3) in /Library/WebServer/Documents/ Websites/forestgumpsays/wp-includes/pluggable.php on line 391

After looking at many similar error posts I figured out the problem. This is what it means. On index.php line3 there is an error indicated. However the problem is that the <?php tag hs a line space before it. Or the <? tag has a space after it. The odd part is that it was only showing an error when I hit the non www domain name. So check the file indicated in the first part of the error. The pluggable.php file is fine it is the one catching the error.

I also had a similar error problem on a new wordpress install in the config file. Turns out that there was an extra line at the end of the document. I hope this post helps the next person to quickly fix their similar php error problem.