To test I set up a clean WordPress install 4.8.1 with only plugins activated Meta Box 4.12.3 and Meta Box Group 1.0.6.
I used the sample code from the documentation and get this error:
Notice: Undefined index: field_name in /Users/wh/MAMP/test-wp/wordpress/wp-content/plugins/meta-box-group/class-rwmb-group-field.php on line 59
Fatal error: Uncaught Error: Call to undefined method RW_Meta_Box::get_class_name() in /Users/wh/MAMP/test-wp/wordpress/wp-content/plugins/meta-box-group/class-rwmb-group-field.php:61 Stack trace: #0 /Users/wh/MAMP/test-wp/wordpress/wp-content/plugins/meta-box/inc/field.php(539): RWMB_Group_Field::html(Array, Array) #1 /Users/wh/MAMP/test-wp/wordpress/wp-content/plugins/meta-box/inc/clone.php(56): RWMB_Field::call(Array, 'html', Array) #2 /Users/wh/MAMP/test-wp/wordpress/wp-content/plugins/meta-box/inc/field.php(64): RWMB_Clone::html(Array, Array) #3 /Users/wh/MAMP/test-wp/wordpress/wp-content/plugins/meta-box/inc/field.php(539): RWMB_Field::show(Array, false, 32) #4 /Users/wh/MAMP/test-wp/wordpress/wp-content/plugins/meta-box/inc/meta-box.php(225): RWMB_Field::call('show', Array, false, 32) #5 /Users/wh/MAMP/test-wp/wordpress/wp-admin/includes/template.php(1050): RW_Meta_Box->show(Object(WP_Post), Array) #6 /Users/wh/MAMP/test-wp/wordpress/wp-admin/edit-form-advanced.php(702): do_meta_boxes(Object(WP_Screen), 'normal', O in /Users/wh/MAMP/test-wp/wordpress/wp-content/plugins/meta-box-group/class-rwmb-group-field.php on line 61
.
