Hi,
This was an error that came up when a duplicated registration was shown last week.
From debug.log
[11-Nov-2016 06:04:27 UTC] WordPress database error Duplicate key name ‘location_type_code’ for query ALTER TABLE wp_woocommerce_tax_rate_locations ADD KEY location_type_code (location_type(40),location_code(90)) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta
[11-Nov-2016 06:04:27 UTC] WordPress database error Duplicate key name ‘location_type_code’ for query ALTER TABLE wp_woocommerce_shipping_zone_locations ADD KEY location_type_code (location_type(40),location_code(90)) made by require(‘wp-blog-header.php’), require_once(‘wp-load.php’), require_once(‘wp-config.php’), require_once(‘wp-settings.php’), do_action(‘init’), call_user_func_array, WC_Install::check_version, WC_Install::install, WC_Install::create_tables, dbDelta
Thanks,
Lisa