session_start() error

I'm getting this session_start() error.

Warning: session_start() [function.session-start]: open(/var/chroot/home/content/k/l/o/klopez/tmp/sess_86a6f7ac25932e90e42be643d1025487, O_RDWR) failed: No such file or directory (2) in /home/content/k/l/o/klopez/html/obaiti/wp-content/plugins/marketpress/marketpress.php on line 850

Any idea of how to fix it?

It appears in the top of the sliding shopping cart widget of my gridmarket template.

Thanks,