PHP: illegal session id

Question

Possible Duplicate:
Session hijacking or attack?

Lately I am receiving following error on my site

PHP Warning:  session_start(): The session id is too long or contains illegal characters, valid characters are a-z, A-Z, 0-9 and '-,'

This error occurs on this line session_start() does anybody have idea why its happening?

Thanks

Answer 1

http://www.php.net/manual/en/function.session-start.php#82957