Many cases are caused duplicate title in wordpress CMS, usually occur after installing certain plugins and then after it happened duplicate titles, and as a solution, there is a simple way to remove or eliminate the duplicate title. the solution is very easy to fix as follows:
Go to wordpress admin then edit the file head.php in theme editor. find the <title>
The following code at the title that is our theme. (every theme is different but essentially the same)
<title> <? php bloginfo ('name'); ?> <? Php wp_title (''); ?> </ title>
<title> <? php wp_title (''); ?> </ title>
So only a single line of code that you need to change, and if there are other lines of code you have to changeit to <title> <? php wp_title (''); ?> </ title>.
May this article usefull to you. Thanks