I experienced the same Admin lockout as @HeleneWallis after installing the Winchester Responsive v.2.0 (14 Feb 2021) template.

My installation is a fresh Zen Cart 1.57c on PhP 7.4 with MySQL 5.7.
No other Zen Cart plugins or alterations were installed.

My debug log file was showing this fatal error:

--> PHP Fatal error: 1067:Invalid default value for 'date_added' :: CREATE TABLE IF NOT EXISTS flexible_footer_menu(
page_id int(11) NOT NULL AUTO_INCREMENT,
language_id int(11) NOT NULL DEFAULT '1',
page_title varchar(64) CHARACTER SET utf8 NOT NULL DEFAULT '',
page_url varchar(255) CHARACTER SET utf8 DEFAULT NULL,
col_header varchar(64) CHARACTER SET utf8 DEFAULT NULL,
col_image varchar(254) CHARACTER SET utf8 NOT NULL DEFAULT '',
col_html_text text CHARACTER SET utf8,
status int(1) NOT NULL DEFAULT '0',
col_sort_order int(11) NOT NULL DEFAULT '0',
col_id int(11) NOT NULL DEFAULT '0',
date_added datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
last_update datetime DEFAULT NULL,
PRIMARY KEY (`page_id`)
I am going to agree with the observation by @lat9 on this:

Quote Originally Posted by lat9 View Post
Noting that I've seen a bunch of winchester-based sites that include a flexible-footer-menu for which (at least for prior versions) the date_added default is 0000-00-00 00:00:00 (a no-no for strict MySQL installations).
After comparing code to that from the separate Flexible Footer Multilingual installer, this is the fix that worked for me:
1. Install fresh version of Zen Cart 1.57c.
2. Before installing the Winchester Responsive 2.0 template, make this change to this one file the installation package:

In the includes/templates/winchester_responsive_2.0/files/YOUR_ADMIN/includes/installers/winchester_responsive/1_0.php on line 139 change:

Code:
date_added datetime NOT NULL DEFAULT '0000-00-00 00:00:00',
to

Code:
date_added datetime NOT NULL DEFAULT '0001-01-01 00:00:00',

Follow the usual Winchester Responsive installation procedure (upload files, choose template, reset layout boxes).