Hi, I had the same problem installing this plugin on WP2.3. I found the solution on the web –
In the file “wpomatic.php” which is located in the main folder from the original zip file (which btw should be located here)
[root] /wp-content/plugins/wp-o-matic/
On line 121, the admin file is incorrectly referenced.
In the original file line 121 points to:
/wp-admin/admin-db.php
but admin-db.php does not exist.
change this file to “admin.php”
(Credit to Christian Hochfilzer who posted this fix at the author’s site: https://devthought.com/wp-o-matic-the-wordpress-rss-agreggator/)