Error received after installing Pop Up Pro

I received this error in the header of my pages after installing Pop Up Pro. Any ideas what I should do?

Open(/tmp/sess_a5bf6454f7578ad53479356449a2e6f4, O_RDWR) failed: Permission denied (13) in /home/setter/public_html/wp-content/plugins/popover/inc/external/wpmu-lib/inc/class-thelib.php on line 114

Warning: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/setter/public_html/wp-content/plugins/popover/inc/external/wpmu-lib/inc/class-thelib.php:114) in /home/setter/public_html/wp-content/plugins/popover/inc/external/wpmu-lib/inc/class-thelib.php on line 114