Stoan

I switched on logging for this so pasting the total result here.

[10-Feb-2022 19:02:58 UTC] PHP Deprecated:  Required parameter $participant_id follows optional parameter $post in /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/xnau_FormValidation.php on line 96
[10-Feb-2022 19:03:25 UTC] PHP Deprecated:  Required parameter $participant_id follows optional parameter $post in /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/xnau_FormValidation.php on line 96
[10-Feb-2022 19:03:25 UTC] PHP Fatal error:  Uncaught TypeError: array_search(): Argument #2 ($haystack) must be of type array, null given in /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_FormElement.php:451
Stack trace:
#0 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_FormElement.php(451): array_search('null_select', NULL)
#1 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/xnau_FormElement.php(756): PDb_FormElement->_set_null_select()
#2 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/xnau_FormElement.php(288): xnau_FormElement->_dropdown()
#3 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_FormElement.php(172): xnau_FormElement->call_element_method()
#4 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/xnau_FormElement.php(244): PDb_FormElement->build_element()
#5 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_FormElement.php(54): xnau_FormElement->__construct(Array)
#6 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_FormElement.php(95): PDb_FormElement->__construct(Array)
#7 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_Field_Editor.php(770): PDb_FormElement::get_element(Array)
#8 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_Field_Editor.php(195): PDb_Field_Def_Parameter->html()
#9 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_Field_Editor.php(63): PDb_Field_Editor->get_att_control('default')
#10 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_Manage_Fields.php(193): PDb_Field_Editor->get_next_control()
#11 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_Manage_Fields.php(150): PDb_Manage_Fields::field_editor_html('which_event_do_...')
#12 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_Manage_Fields.php(97): PDb_Manage_Fields->print_group_tab_content('main')
#13 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_Manage_Fields.php(58): PDb_Manage_Fields->print_group_tabs()
#14 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/manage_fields.php(10): PDb_Manage_Fields->__construct()
#15 /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/participants-database.php(832): include('/usr/www/users/...')
#16 /usr/www/users/iomzavvpac/wp-includes/class-wp-hook.php(307): Participants_Db::include_admin_file('')
#17 /usr/www/users/iomzavvpac/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters('', Array)
#18 /usr/www/users/iomzavvpac/wp-includes/plugin.php(474): WP_Hook->do_action(Array)
#19 /usr/www/users/iomzavvpac/wp-admin/admin.php(259): do_action('participants-da...')
#20 {main}
  thrown in /usr/www/users/iomzavvpac/wp-content/plugins/participants-database/classes/PDb_FormElement.php on line 451

Thanks for the reply.
I have disabled all plugins and also tried other options items such as radio buttons, drop down/other, radio buttons/other, to no avail.
The only way I can get pass that point is to delete the drop-down entry in the database to get back into the Participant Info Fields page.

See screen grab here

Thanks I got it to work. A hard refresh was needed.