¡Hola! he encontrado lo que te copio aquí en el enlace
http://codex.wordpress.org/FAQ_Troubleshooting#How_do_I_solve_the_Headers_already_sent_warning_problem.3F
How do I solve the Headers already sent warning problem?
Description: You get a warning message on your browser that says:
Warning: Cannot modify header information – headers already sent by (output started at
Reason and Solution :
It is usually because there are spaces, new lines, or other stuff before an opening <?php tag or after a closing ?> tag, typically in wp-config.php. This could be true about some other file too, so please check the error message, as it will list the specific file name where the error occurred (see «Interpreting the Error Message» below). Replacing the faulty file with one from your most recent backup or one from a fresh WordPress download is your best bet, but if neither of those are an option, please follow the steps below.
Just because you cannot see anything does not mean that PHP sees the same.
Download the file mentioned in the error message via FTP or the file manager provided in your host’s control panel.
Open that file in a plain text editor (NOT MS Word or similar. Notepad or BBEdit are fine).
Check that the very first characters are <?php
Check that the very last characters are ?>
To be sure about the end of the file, do this:
Place the cursor between the ? and >
Now press the DELETE key on your computer
Note to MAC users: The «DELETE» key on a PC deletes characters to the right of the cursor. That is the key noted here.
Keep that key pressed
For at least 15 seconds
Now type > and
save without pressing any other key at all.
If you press another key, you will bring the problem back.
Upload the file back to your server after editing and saving the file.
Note: Also check the encoding of the file. If the file is encoded as UTF-8 with BOM, the BOM is seen as a character which starts the output.
Interpreting the Error Message:
If the error message states: Warning: Cannot modify header information – headers already sent by (output started at /path/blog/wp-config.php:34) in /path/blog/wp-login.php on line 42, then the problem is at line #34 of wp-config.php, not line #42 of wp-login.php. In this scenario, line #42 of wp-login.php is the victim. It is being affected by the excess whitespace at line #34 of wp-config.php.
If the error message states: Warning: Cannot modify header information – headers already sent by (output started at /path/wp-admin/admin-header.php:8) in /path/wp-admin/post.php on line 569, then the problem is at line #8 of admin-header.php, not line #569 of post.php. In this scenario, line #569 of post.php is the victim. It is being affected by the excess whitespace at line #8 of admin-header.php.
Other issues that might cause that error:
In case you’ve used the function: wp_redirect() or tried to use a header redirect after the header (or any content at all was sent) that error message will pop. Instead use javascript redirection if needed.
GRACIAS/THANK YOU a zoonini – help me help you que colgó este enlace hace 10 meses.
Al realizar esta operación desaparecieron errores pero aparecieron otros. tiene que ver con el código del archivo en cuestión. Te recomiendo que hagas búsquedas del error (si sale y esperemos que no). Como yo estoy peleando con el error «Parse error: syntax error, unexpected T_STRING», te mando algunos enlaces. Ojalá no tengas que usarlos: http://codex.wordpress.org/Editing_wp-config.php; http://wordpress.org/support/topic/parse-error-syntax-error-unexpected-t_string-25?replies=6
Suerte!
