Error message on dashboard after activating a plugin

Hi!

I've installed a plugin called revolution slider, and when I activate it I get the error message below at the top of my wordpress dashboard:
"Warning: session_start() [function.session-start]: open(/tmp/sess_X5mL3BpsgSpsHzrZywedK2, O_RDWR) failed: Permission denied (13) in /home/wheelofcommerce/wheelofcommerce.com/wp-content/plugins/revslider/revslider_admin.php on line 43

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/wheelofcommerce/wheelofcommerce.com/wp-content/plugins/revslider/revslider_admin.php:43) in /home/wheelofcommerce/wheelofcommerce.com/wp-content/plugins/revslider/revslider_admin.php on line 43"

How do I fix this?

Thanks.