Standard install of v1.5.7c - with Responsive Classic Template

When I try to reset a password from the admin panel I get a 500 error. This is what comes up in my error logs -

v1.5.7c

[28-Jun-2022 21:49:24 America/New_York] PHP Fatal error: Uncaught Error: Call to undefined function zen_admin_demo() in path/path/other/customers.php:312
Stack trace:
#0 x/x/x/index.php(11): require()
#1 {main}
thrown in /x/x/xcustomers.php on line 312/

[28-Jun-2022 21:49:24 America/New_York] Request URI: x/x/index.php?cmd=customers&page=1&action=pwdresetconfirm, IP address: xx.x.x.x.
--> PHP Fatal error: Uncaught Error: Call to undefined function zen_admin_demo() in x/x/x/customers.php:312
Stack trace:
#0 /x/x/x/x/index.php(11): require()
#1 {main}
thrown in /x/x/x/x/customers.php on line 312.


Im thinking the _demo part of the function zen_admin_demo is the problem but I'm not sure what the correct callout is.

Help!