All mysql_* functions were removed in PHP 7, use an updated theme or contact the author.

You can check here itube.co.in

I am using latest theme update.

I have installed social locker plugin & active. Then I found above error.

mysql* commands have been removed in PHP7 and have been depreciated (not recommended for use) since PHP 4.3.0 (Released: 27 December 2002). I am guessing that someone edited this from the default twentysixteen/functions.php file since it does not include a mysqlescape_string() command.

mysqlirealescape_string() provides a drop in replacement under the mysqli module (installed in package php7.0-mysql) that should help you resolve this. I would also recommend looking for any other mysql_ type calls in your theme to ensure they are updated or removed.