Erro em session_start()

Galera alguem pode me ajudar com esse erro abaixo

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Warning: session_start() [function.session-start]: Cannot send session cookie - headers already sent by (output started at /public_html/acompanhamento.php:1) in /public_html/acompanhamento.php on line 2

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /public_html/acompanhamento.php:1) in /public_html/acompanhamento.php on line 2

Valeu galera