I've just submitted v2.2.0 of the IP Blocker to the plugin moderators for review and will post back here once it's available (https://www.zen-cart.com/downloads.php?do=file&id=1814) for download.

This release contains changes associated with the following GitHub issues. Note that support is dropped for Zen Cart versions prior to 1.5.6!

#12: Correct use of PHP's serialize function.
#13: Correct "special_login" page location; issue when store is installed in a sub-directory.
#14: Restructure, using HTML5 for zc156+.
#15: Reduce changes to `whos_online.php` (1 change section).
#16: Correct MySQL error on initial install.
#17: Use the built-in `zen_get_ip_address` to retrieve the current IP address.
#18: Automatically block addresses found invalid by `zen_get_ip_address`
#19: Remove unused fields from the database table.
#20: Admin: Use PHP's `val_function` to validate any entered IP address.
#21: Add language-constant to contain the `special_login` page's instructions.
#22: No exit, now, from the `special_login` page if the configured password is blank/empty.
#23: Simplify storefront checks for wildcard IP address ranges.
#25: Admin: Display the password (hashed) as a simple input field instead of a password one.