Apache error: Address already in use: make_sock: could not bind to address [::]:443

Apache error while starting:

Address already in use: make_sock: could not bind to address [::]:443

*Executing start method ("/lib/svc/method/http-apache2 start") ]
(125)Address already in use: make_sock: could not bind to address [::]:443
no listening sockets available, shutting down
Unable to open logs*

Listen 443 is added in ssl.conf.
Listen 80 is added in httpd.conf.

HTTPD.conf file:

DocumentRoot "/var/apache2/htdocs"
<Directory />
    Options FollowSymLinks
    AllowOverride All
</Directory>
<Directory "/var/apache2/htdocs">
    Options Indexes FollowSymLinks
    AllowOverride All
    Order allow,deny
    Allow from all
</Directory>

Also getting the following error in error_log file:

configuration error:  couldn't perform authentication. AuthType not set!:index.html**
index.html's location : /var/apache2/htdocs

Thanks in advance

1. Files defined inside conf.d would have Listen port as 443 multiple times in multiple files which can cause this issue.
2. Seems port 443 is used by some other process, it can be checked by "netstat -anp|grep :443"