I have this message when I try to add a new variation of a product on Woocommerce/WP:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, array must have exactly two members in /home/souffle/public_html/wp-includes/class-wp-hook.php on line 288

This kind of message appears when I log into my admin account and other places too, since two days.

Can someone help me?