"Headers already sent by..." error message
 

Whenever you get this message, remove any blank lines you may have outside of opening <?php and closing ?> PHP tags in one of the files mentioned in the error message, or in /themes/atahualpa/functions.php (a Atahualpa file) or in /wp-config.php (a core Wordpress file), especially at the bottom of these files.

FILE STARTS HERE
remove blank line (or space) here, if any
<?php
...

blank lines are o.k. here

...
?>
remove blank line (or space) here, if any
<?php
...

blank lines are o.k. here

...
?>
remove blank line (or space) here, if any
FILE ENDS HERE