This is normally caused by one of two reasons:
Did you add the entry to the language file
i.e. add :
define('BOX_CONFIGURATION_ECOMMERCEBROWSER', 'Facebook eCommerce Browser');
To the bottom of /admin/includes/languages/english.php
Alternatively the MySQL script has failed to find the original configuration group created by the first install script and as a result the insert fails. To manually find the configuration_group_id:
SELECT configuration_group_id FROM configuration_group WHERE configuration_group_title= 'Facebook Catalog Browser'
Then you need to create a new entry in the admin_pages table, with the ID found above inserted into the 2 locations INSERT_ID_HERE :
INSERT INTO admin_pages (page_key,language_key,main_page,page_params,menu_key,display_on_menu,sort_order)
VALUES ('configeCommerceBrowser','BOX_CONFIGURATION_ECOMMERCEBROWSER','FILENAME_CONFIGURATION','gID=INSERT_ID_HERE','configuration','Y',INSERT_ID_HERE);
P.s. You will need to revert the manual password you added, back to the original format, otherwise the setting in the Zencart admin will be ignored.