Php Error conflicts with Tribulant Newsletter Plugin

Hi,
I have the Developer Bundle. Metabox plugin since a latest update is causing an error and so it is compromising the Newsletter Tribulant Plugin (https://tribulant.com/plugins/view/1/wordpress-newsletter-plugin).
This is the error that Metabox is causing:

Catchable fatal error:
Argument 1 passed to RWMB_Core::add_context() must be an instance of WP_Post, null given in /home/ln2gjrij/public_html/wp-content/plugins/meta-box/inc/core.php on line 112

Can you release a fast fix please?
Because we cannot send any newsletter.
Screenshot of the newsletter page: https://screenshots.firefox.com/uEikJ0kKg0uyrF4Y/www.nuove-esperienze.it