Support

Please follow the instructions on https://www.akeeba.com/documentation/admin-tools-joomla/athtaccess500.html

Let's make sure that the problem is indeed caused by Admin Tools. In order to do so, try the following:

Try to replicate the issue after disabling the "System - Admin Tools" plugin. If you can still replicate the issue, it is not caused by Admin Tools. Disabling that plugin means that Admin Tools code (including the Web Application Firewall) is not running on your site.

If doing any of the above resulted in the issue still occurring, it's not related with Admin Tools and we can't help you. If doing any of the above did stop the issue from occurring, we'll have to do some troubleshooting.

First go to Admin Tools, Web Application Firewall, Configure WAF. Make sure "Log security exceptions" is set to Yes; if it's not, set it to Yes and click on Save. Now try reproducing your issue. Immediately after that, please go to Admin Tools, Web Application Firewall, Security Exceptions Log. The latest log entry at the top should have the date and time of when the issue occurred. Please copy the Reason and Target URL here so that we can further help you.

If, however, you do not see a log entry, or the Date and/or IP address do not match your last access, this problem is not caused by Admin Tools' WAF. In this case, you will have to do some .htaccess troubleshooting. You may need to read the general .htaccess troubleshooting page, as well as the page on finding out necessary .htaccess exceptions.

There was not enough information to go by in your original ticket text. Now that we have all the information, here's what was going on. Two issues are apparent:

1. You had enabled the administrator password protection (.htaccess and .htpasswd files in the administrator folder). That's what my first reply told you to do. You can use that feature but do make sure that you note down the username and password. Also note that some older versions of Apache may only accept passwords up to 8 characters long. If it looks like the server doesn't recognise the password try using one that's only 8 characters long. If that works, your version of Apache is very old and should be replaced.

2. You had enabled the administrator secret URL parameter. If you set it to foobar and your site is https://www.example.com you need to access your administrator login as https://www.example.com/administrator/index.php?foobar (note the bold part). If you forget the secret word yes, one way around it is disabling the plugin from the database, the other is following the instructions in https://www.akeeba.com/documentation/admin-tools-joomla/atwafissues.html

I am not sure why you removed the .htaccess file from the site's root or if your login issues were about the former two points or something else. If it's something else, tell me what was going on so I can help.