problem with session: "Cannot send session cookie"

hi
i write only below code in “index.php”:

[code=php]<?php
session_start();
?>[/code]

but i see this error:

[CODE]Warning: session_start() [function.session-start]: Cannot send session cookie – headers already sent by (output started at J:wampwwwProjectindex.php:1) in J:wampwwwProjectindex.php on line 2
Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at J:wampwwwProjectindex.php:1) in J:wampwwwProjectindex.php on line 2[/CODE]

i don’t send any thing for output but this error is show.
please help me. what i do?

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