Hi lat9,
I did a comparison of the files described in the docs folder of the add-on for News Box Manager v3.0.2, and what files are actually included.
I think the main problem might be an incorrectly-named definition file? Not sure about the mismatch of the various files, so will wait for confirmation.

As listed in docs
(I marked as OK if the described files were actually there)
OK: /includes/classes/observers/auto.news_box_manager_metatags.php
Does not exist---wrong Name?: /includes/extra_datafiles/news_box_manager_file_database_names.php
OK: /includes/languages/english/all_articles.php
OK: /includes/languages/english/article.php
OK: /includes/languages/english/extra_definitions/news_box_manager_defines.php
OK: /includes/modules/news_box_format.php
OK: /includes/modules/pages/all_articles/header_php.php
OK: /includes/modules/pages/article/header_php.php
OK: /includes/modules/pages/more_news/header_php.php
OK: /includes/modules/pages/news_archive/header_php.php
OK: /includes/modules/sideboxes/news_box_sidebox.php
OK: /includes/templates/template_default/sideboxes/tpl_news_box_sidebox.php
Does not exist: /includes/templates/template_default/sideboxes/tpl_news_box_sidebox2.php
OK: /includes/templates/template_default/templates/tpl_modules_news_box_format.php
OK: /includes/templates/template_default/templates/tpl_all_articles_default.php
OK: /includes/templates/template_default/templates/tpl_article.php
OK: /includes/templates/YOUR_TEMPLATE/css/stylesheet_news_box_manager.css
OK: /includes/templates/YOUR_TEMPLATE/templates/tpl_index_default.php
OK: /YOUR_ADMIN/news_box_manager.php
OK: /YOUR_ADMIN/includes/auto_loaders/config.news_box_manager.php
OK: /YOUR_ADMIN/includes/extra_datafiles/news_box_manager_file_database_names.php
OK: /YOUR_ADMIN/includes/extra_datafiles/news_box_manager_sanitization.php
OK: /YOUR_ADMIN/includes/init_includes/init_news_box_manager_admin.php
OK: /YOUR_ADMIN/includes/languages/english/news_box_manager.php
OK: /YOUR_ADMIN/includes/languages/english/extra_definitions/news_box_manager_menu_name.php

Files existing but not described in docs:
/YOUR_ADMIN/news_box_manager1.php
/YOUR_ADMIN/news_box_manager2.php
/YOUR_ADMIN/news_box_manager3.php
/YOUR_ADMIN/news_box_manager4.php
/YOUR_ADMIN/includes/classes/observers/NewsBoxManagerAdminObserver.php
/YOUR_ADMIN/includes/functions/news_box_manager_functions.php
/YOUR_ADMIN/includes/init_includes/init_news_box_manager_install.pph
/YOUR_ADMIN/includes/init_includes/init_news_box_manager_update.php
Possibly wrong name?: /includes/extra_datafiles/news_box_file_database_names.php
/includes/modules/sideboxes/news_box_sidebox2.php
/includes/templates/YOUR_TEMPLATE/jscript/jscript_sidebox_slider.js