[Php-avanzado] A session had already been started

[Silverzero]

Me estaba logueando y se corto la conexión, y le di al botón de vuelta
para ingresar y me aparece esto:

Notice: A session had already been started - ignoring session_start()
in ... on line 143

Warning: Cannot modify header information - headers already sent by
(output started at ... on line 149

Como evito que pase esto?

-- 
Carolina Derromediz
Cel. +54 223 5301599