With debugging turned on, I'm getting the following error:

The block ajax_marking does not define the standard capability block/ajax_marking:addinstance
line 606 of /blocks/moodleblock.class.php: call to debugging()
line 584 of /blocks/moodleblock.class.php: call to block_base->has_add_block_capability()
line 1090 of /lib/blocklib.php: call to block_base->user_can_addto()
line 1047 of /lib/blocklib.php: call to block_manager->user_can_delete_block()
line 256 of /blocks/moodleblock.class.php: call to block_manager->edit_controls()
line 951 of /lib/blocklib.php: call to block_base->get_content_for_output()
line 1003 of /lib/blocklib.php: call to block_manager->create_block_contents()
line 353 of /lib/blocklib.php: call to block_manager->ensure_content_created()
line 7 of /theme/intro_to_business/layout/general.php: call to block_manager->region_has_content()
line 847 of /lib/outputrenderers.php: call to include()
line 777 of /lib/outputrenderers.php: call to core_renderer->render_page_layout()
line 243 of /course/view.php: call to core_renderer->header()