How can I stop Prestashop from generating 404 error to legit URL?

[Walrus]

I have a third-party PHP-based newsletter script installed in the root where Prestashop is also installed.

 

When I try to access the newsletter editor, Prestashop generates a 404 page not found error. How do I bypass the error? 

 

The folder and all its files are present. The path is of the order:

 

http://mydomain.com/newsmaker/admin1234/news.php

 

Thanks.