Your solution
Fatal error: Uncaught Error: Function name must be a string in …
app\code\core\Mage\Core\Model\Layout.php:555 …
This error was easy to fix because the problem was in the following line:
$out .= $this->getBlock($callback[0])->$callback[1]();
Instead it should be:
$out .= $this->getBlock($callback[0])->{$callback[1]}();
find your detail solution here on below given link
http://www.code007.ro/making-work-magento-with-php-7-rc1/