Warnings : cannot send cookie, cannot modify header information

Hola, he restaurado mi sitio web joomla en mi servidor:

– he creado la base de datos, tiene todos los contenidos (y6z4i_content, y6z4i_menu, y6z4i_sections…..)
– he hecho los cambios en el archivo de configuración $host, $db,$user, $password…
– he subido todos los archivos con Filezilla, incluida la copia de seguridad
– he cambiado las rutas de log y tmp

a la hora de ir tanto al frontend como al backend….me salen los siguientes warnings

Warning: session_start() [function.session-start]: Cannot send session cookie – headers already sent by (output started at /home/content/v/o/l/voluntariadoma/html/configuration.php:1) in /home/content/v/o/l/voluntariadoma/html/libraries/joomla/session/session.php on line 423

Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /home/content/v/o/l/voluntariadoma/html/configuration.php:1) in /home/content/v/o/l/voluntariadoma/html/libraries/joomla/session/session.php on line 423

Warning: Cannot modify header information – headers already sent by (output started at /home/content/v/o/l/voluntariadoma/html/configuration.php:1) in /home/content/v/o/l/voluntariadoma/html/libraries/joomla/session/session.php on line 426

Warning: Cannot modify header information – headers already sent by (output started at /home/content/v/o/l/voluntariadoma/html/configuration.php:1) in /home/content/v/o/l/voluntariadoma/html/templates/ja_purity/ja_templatetools.php on line 44

Cómo puedo solucionarlos??? en qué repercuten??