Captcha image does not appear

The captcha was working until a few months ago when it stopped showing the captcha image. When I try to see only the image via its url I get a bunch of errors.

I am using W3 cache.

Thanks,

_____

Warning: session_start() [function.session-start]: open(/home/tmp/sessions_tmp/sess_00877895f1bf5b8979b56d50ebc4d5bc, O_RDWR) failed: No such file or directory (2) in /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php on line 482

Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php:482) in /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php on line 482

Warning: Cannot modify header information – headers already sent by (output started at /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php:482) in /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php on line 1003

Warning: Cannot modify header information – headers already sent by (output started at /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php:482) in /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php on line 1004

Warning: Cannot modify header information – headers already sent by (output started at /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php:482) in /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php on line 1005

Warning: Cannot modify header information – headers already sent by (output started at /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php:482) in /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php on line 1006

Warning: Cannot modify header information – headers already sent by (output started at /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php:482) in /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php on line 1007

Warning: Cannot modify header information – headers already sent by (output started at /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php:482) in /home/marcelo/public_html/wp-content/plugins/si-captcha-for-wordpress/captcha/securimage.php on line 1023
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http://wordpress.org/extend/plugins/si-captcha-for-wordpress/