apparently it has to do with the way Apache looks at the index.php file. The following is from the post by k.v.ahuja.
Solution 1
If allowed by your host, putting this in an .htaccess file will solve the problem:
DirectoryIndex index.html index.htm index.php
Solution 2
Some hosts allow you to make a change, via their hosting control panel, to the DirectoryIndex. It’s typically described as Indexes or Index documents, but may also require you to type something like
DirectoryIndex index.html index.htm index.php
or specify index.php as an index type file.
Solution 3
Instruct Apache to treat index.php as an index file. If you own the server, or have access to the http.conf file, simply modify the DirectoryIndex line in httpd.conf to:
DirectoryIndex index.html index.htm index.php
This search of the forum found the solutions described above:
https://www.ads-software.com/search/displays+directory?forums=1
