Warning session_start(): Error

I installed the most recent version of the plugin and received this error message:

warning: session_start() : open(/var/php_sessions/sess_d105aad9b8dd5ab5c325ffee8007400, O_rdwr)
/hermes/bosnaweb05a/b2510/ipg.technicallinknet/wp-content/plugins/cta/classes/class.cta.variations.php on line 38

At the top of the page after activating the plugin. It looks like i can use the plugin but the message concerns me. any information would be helpful. I have deactivated the plugin for now.

https://wordpress.org/plugins/cta/