The secret word is applied by the Admin Tools plugin. By renaming the main.php file you are disabling the plugin. Also, if the feature is enabled, if you try to access the site's backend login page without the correct secret word you are simply redirected to the frontend.
Your problem is with the administrator password protection. First, how to fix that. Use FTP or your host's control panel file manager to go into your site's administrator folder. Make sure you have set up your FTP client of the host's control panel file manager to display hidden files. Delete the .htaccess and .htpasswd files from the administrator folder. Now you can access your site.
Why did you have that problem? It is NOT a bug in Admin Tools, it is a configuration issue with your host. Please contact your host and paste them the following paragraph so they can fix it:
Hello. I have tried to apply password protection to my site's administrator folder using .htaccess and .htpasswd. However, upon trying to access that folder I get a 404 error. My developer explained to me that this happens because you have set up custom error pages on Apache. Therefore, when Apache tries to send an HTTP 401 Authentication Required status to the browser it sees that there is a custom page to display it. Since the file does not actually exist, Apache converts this to a 404 Not Found. Please disable custom error pages in Apache or tell me how I can do that myself. Thank you.
Nicholas K. Dionysopoulos
Lead Developer and Director
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