I'm in the process of updating a site that uses version

// $Id: backup_mysql.php revised 2012-07-07 $

... and updating to the most recent version:

// $Id: backup_mysql.php revised 2020-07-19 $

The issue that I'm having is that I'm receiving a 1045 (access denied) when attempting to perform a backup with the latest version, but the database properly 'backs up' using the older version (albeit without gzip compression, even though I've ticked that checkbox). I'm not sure what additional information might be needed to aid in this issue's resolution, but here goes.

The (test) site's running in a sub-directory off the main site, e.g. https://www.example.com/test. As I'm trying to get the majority of the plugins updated prior to the Zen Cart upgrade, that test site's currently running zc155e on PHP v5.6.40 with MySQL 5.7.23-23 (NO_AUTO_CREATE_USER, NO_ENGINE_SUBSTITUTION).

There's no /admin/includes/local/configure.php file that could be messing with the configuration and I'm not seeing any major change in the processing that "should" affect the outcome.