Error message

Hello,
I’have a big problem with my last website. I do it last week, and all is ok. Tomorrow I enter and I see this error message.
I do anything in this two day. Why there is this erros? What it’s happened?
I read some ather post about similar error, that there is prblem with the hosting permission. Is it?

May you help me to understand, thanks!

This is the error messages:

Warning: session_start(): open(/var/lib/php/session/sess_864ba5ffc513d658e1c8c60420d26d5a, O_RDWR) failed: Permission denied (13) in /home/agrieco/agriturismoeco.it/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php on line 32

Warning: session_start(): Cannot send session cookie – headers already sent by (output started at /home/agrieco/agriturismoeco.it/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php:32) in /home/agrieco/agriturismoeco.it/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php on line 32

Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at /home/agrieco/agriturismoeco.it/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php:32) in /home/agrieco/agriturismoeco.it/wp-content/themes/enfold/config-templatebuilder/avia-shortcodes/masonry_entries.php on line 32

Warning: Unknown: open(/var/lib/php/session/sess_864ba5ffc513d658e1c8c60420d26d5a, O_RDWR) failed: Permission denied (13) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/session) in Unknown on line 0