This is definitely a hosting issue and not a scripting issue.
The problem is exactly what the error says that it is: "Failed to write session data (files). Please verify that the current setting of session.save_path is correct"
It means the session.save_path setting in the php.ini file is set to a non-existent folder or one that doesn't have the proper permissions.
Most likely any script that tries to set a session variable would produce the same error... Try a simple script on a new page like:
$_SESSION['test_sessions'] = 'saved value';
Do you get the same error? If so, you will have to go back to your hosting company and show them this simple page and they won't be able to avoid it.