10.11.10 23:38:13  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_ok'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_bar'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_list_2'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_screen'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\connected\gametype_select_screen_wrapper'
10.11.10 23:38:13  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:13  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:13  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_ok'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_bar'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_list_2'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_screen'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\connected\gametype_select_screen_wrapper'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\mp_map_select\mp_map_select_button_ok'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\mp_map_select\mp_map_select_button_bar'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\mp_map_select\mp_map_select_list_2'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\mp_map_select\mp_map_select_screen'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\split_screen\splitscreen_map_select_wrapper'
10.11.10 23:38:13  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\split_screen\splitscreen_map_select_postgame_wrapper'
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_ok'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_bar'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_list_2'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_screen'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\connected\gametype_select_screen_wrapper'
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_ok'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_bar'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_list_2'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_screen'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\connected\gametype_select_screen_wrapper'
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  the ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen' (tags\ui\shell\main_menu\multiplayer_type_select\server_settings\server_settings_screen.ui_widget_definition) had an invalid header
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_ok'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_button_bar'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_list_2'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\gametype_select\gametype_select_screen'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\connected\gametype_select_screen_wrapper'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\mp_map_select\mp_map_select_button_ok'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\mp_map_select\mp_map_select_button_bar'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\mp_map_select\mp_map_select_list_2'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\mp_map_select\mp_map_select_screen'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\connected\connected_map_select_wrapper'
10.11.10 23:38:14  failed to load ui_widget_definition tag 'ui\shell\main_menu\multiplayer_type_select\connected\connected_map_select_postgame_wrapper'
10.11.10 23:38:14  failed to load ui_widget_collection tag 'ui\shell\main_menu'
10.11.10 23:38:14  failed to load tag_collection tag 'ui\ui_tags_loaded_mainmenu_scenario_type'
10.11.10 23:38:14  failed to load ui tags tied to the main menu scenario
10.11.10 23:38:14  WARNING: 1 clusters in structure_bsp levels\ui\ui have no background sound or sound environment.

Just One-Seventeenth of a huge load of error lines. They seem to load up in guerilla fine.
How do I fix it?

i would suggest extracting every tag from one of the original halo ce maps and the ui map.

That's where i got these, and then i tried a backup of some older tags and it failed too.