ZC156c Admin - Unable to edit prducts or add new product

http://www.healthybird.net
ZCv156c, PHP 7.2.14
Plugins = Stock by Attrributes Combined, Canada Post, recover cart sales

I recently upgraded from 1.5.6a to 1.5.6c. Now I've discovered the following error when attempting to edit a product; or add a new product
Error!
Unable to determine the page link!
Function used:
zen_href_link('', 'cPath=64_165&product_type=1&pID=1380&action=new_product_preview', 'NONSSL')

I can edit product catefories without difficulty
The following debug log error attached

[14-Oct-2019 16:35:52 UTC] Request URI: /catalog/nnnnnnnnnnn/product.php?action=new_product, IP address: 174.116.220.172
#1 trigger_error() called at [/home/healt244/public_html/catalog/nnnnnnnnnnn/includes/functions/html_output.php:16]
#2 zen_href_link() called at [/home/healt244/public_html/catalog/nnnnnnnnnnn/includes/functions/html_output.php:181]
#3 zen_draw_form() called at [/home/healt244/public_html/catalog/nnnnnnnnnnn/includes/modules/product/collect_info.php:246]
#4 require(/home/healt244/public_html/catalog/nnnnnnnnnnn/includes/modules/product/collect_info.php) called at [/home/healt244/public_html/catalog/nnnnnnnnnnn/product.php:101]
--> PHP Fatal error: zen_href_link(, cPath=64_163&action=new_product_preview, NONSSL), unable to determine the page link. in /home/healt244/public_html/catalog/nnnnnnnnnnn/includes/functions/html_output.php on line 16.

Where should I look for the correction?

This bug was fixed in 1.5.7. In admin/includes/functions/admin_access.php in function zen_get_admin_menu_for_user() around line 837

change

while (!$result->EOF)
{

to

        while (!$result->EOF) {
            if (defined($result->fields['pageName']) && defined($result->fields['main_page'])) {

I think you will need to go back and carefully merge the stock by attributes files with core files

~Melanie

Stock by Attributes Combined for ZC 1.5.6 only merges with four admin files and the merges are pretty much only to support display of the customid and potential selection of links to get to the SBA tracking panel.

When was the last time a product was attempted to be modified before the latest upgrade? There were some changes made between 1.5.6a and 1.5.6c that might cause this issue if they were missed. Furthermore an issue if the install/upgrade to ZC 1.5.6a wasn't done.