.htaccess/.htpasswd 500 Internal Server Error

If nothing helped and you're using PHP you can make it work by putting this in your index.php (on top):

if (isset($_SERVER['PHP_AUTH_USER']) && isset($_SERVER['PHP_AUTH_PW'])) {
    if ($_SERVER['PHP_AUTH_USER'] != 'user' || 
        $_SERVER['PHP_AUTH_PW'] != 'pass') {

        header('WWW-Authenticate: Basic realm="Protected area"');
        header('HTTP/1.0 401 Unauthorized');

        die('Login failed!');
    }
}

Most likely problem is this line:

AuthUserFile /.htpasswd 

This line should provide full filesystem path to the password file e.g.

AuthUserFile /var/www/.htpasswd 

To discover your filesystem path, you can create a PHP document containing

echo $_SERVER['DOCUMENT_ROOT'];

Permissions can cause this issue too.

Make sure .htpasswd is readable by the web server user.

For instance, if you use nginx check the nginx.conf to find out what the server user is, if you use Apache you can find it out this way, etc.

Then set the right owners and read permissions to .htpasswd