Error in session_start

Suddenly the following error messages started appearing on the top of my blog https://nynjbengali.ethnomediallc.com

Warning: session_start() [function.session-start]: open(/tmp/sess_931c3e27add0adc8044215a6c4e67f26, O_RDWR) failed: Permission denied (13) in /home/sudipta/public_html/wpress/wp-content/plugins/wordpress-automatic-upgrade/wordpress-automatic-upgrade.php on line 92

Warning: session_start() [function.session-start]: Cannot send session cache limiter – headers already sent (output started at /home/sudipta/public_html/wpress/wp-content/plugins/wordpress-automatic-upgrade/wordpress-automatic-upgrade.php:92) in /home/sudipta/public_html/wpress/wp-content/plugins/wordpress-automatic-upgrade/wordpress-automatic-upgrade.php on line 92

What’s causing it?
I noticed that this started since I uploaded wassup plugin zip file and extracted it. But since then I have removed the wassup plugin directory.