wampapache64 service won't start (1 reply)

When starting this service, I get the error:

"Windows could not start the wampapache64 on Local Computer. For more information, review the System Event Log. If this is a non-Microsoft service, contact the service vendor, and refer to service-specific error code 1."

In Event Log, we're Informed that the service has entered the stopped state.


And we get the following error in Windows Logs > System ... source is Service Control M:anager
The wampapache64 service terminated with the following service-specific error:
Incorrect function.

Here's some info:
WampServer 3.1.3
phpMyAdmin 4.7.9
Adminer 4.6.2
Apache 2.4.33
PHP 5.6.35
MySQL 5.7.21

Wamp logo is orange.

In the PHP error log I see this:
[05-May-2021 20:52:21 UTC] Apache variable "${INSTALL_DIR}" is not defined.

In the Apache log I see this at the bottom, with no date, more than 10 times in a row:
AH00016: Configuration Failed