The session save path (/var/lib/php/session) is not set to a valid directory. Check your PHP (php.in

I get this error message on the "All Snapshots" page of the snapshot plugin.

"The session save path (/var/lib/php/session) is not set to a valid directory. Check your PHP (php.ini) settings or contact your hosting provider."

I confirmed using my FTP that this is a valid directory. My host does not support 3rd party plugins.