I've found a conflict with a popular plugin, Mashsharer:
Mashsharer gives me an error message on the edit screen:
Fatal error: Uncaught TypeError: Argument 1 passed to MB_Tabs::opening_div() must be an instance of RW_Meta_Box, instance of MASHSB_RW_Meta_Box given, called in /home/run4ac/public_html/wp-includes/class-wp-hook.php on line 286 and defined in /home/run4ac/public_html/wp-content/plugins/meta-box-tabs/meta-box-tabs.php:73 Stack trace: #0 /home/run4ac/public_html/wp-includes/class-wp-hook.php(286): MB_Tabs->opening_div(Object(MASHSB_RW_Meta_Box)) #1 /home/run4ac/public_html/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters('', Array) #2 /home/run4ac/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array) #3 /home/run4ac/public_html/wp-content/plugins/mashsharer/includes/admin/meta-box/inc/meta-box.php(216): do_action('rwmb_before', Object(MASHSB_RW_Meta_Box)) #4 /home/run4ac/public_html/wp-admin/includes/template.php(1073): MASHSB_RW_Meta_Box->show(Object(WP_Post), Array) #5 /home/run4ac/public_html/wp-admin/edit-form-advanced.php(714): do_meta_boxes(Object(WP_Screen), 'normal', Object(WP_Post)) #6 /home/ in /home/run4ac/public_html/wp-content/plugins/meta-box-tabs/meta-box-tabs.php on line 73
Any help would be great tx.
I've just checked the plugin and found that it bundles Meta Box inside:
However, they don't keep the original version of Meta Box. Instead, they changed the code (prefix in the screenshot above). That might break the compatibility with Meta Box extensions.
If you're using their Pro version, please contact them to either update their code (the modified version of Meta Box) or include the original version of Meta Box.
PS: I've posted a topic on wordpress.org.
The author of the MashSharer replied that the new version on Github has a fix for that:
Please try it.