Server Error – 2 sites on subdirectory

Hello – I can’t get backupwordpress plugin to work with my current configuration of 2 wordpress installations on the same domain:

http://www.example.com (wordpress installation #1) and
http://www.example.com/blog (wordpress installation #2).

If I remove the second installation and set it aside in a temp folder outside the root folder, then the plugin will work.

It would be great if you can design the plugin to handle backing up 2 installations within the same directory. This is the codex that I followed: https://codex.ww.wp.xz.cn/Giving_WordPress_Its_Own_Directory

Or if I’m doing something wrong please let me know. This is the error that is generated, but again, once I temporarily remove the second installation the plugin works ok, therefore it’s not truly a server error:

500 Internal Server Error

Internal Server Error
The server encountered an internal error or
misconfiguration and was unable to complete
your request.
Please contact the server administrator
and inform them of the time the error occurred,
and the actions you performed just before this error.
More information about this error may be available
in the server error log.

Apache Server at chriscouncilphotography.com Port 80

https://ww.wp.xz.cn/plugins/backupwordpress/