View the source and you will see that all the menu items have target=""
That is invalid markup

I am assuming the error is in this code block but I don't really understand it to fix

if ($link !== null && $current->get('target') !== null)
{
	echo "<a" . $linkClass . $dataToggle . " href=\"" . $link . "\" target=\"" . $current->get('target') . "\">" 
		. $iconClass
		. '<span class="sidebar-item-title">' . Text::_($current->get('title')) . "</span></a>";
}
elseif ($link !== null && $current->get('target') === null)
{
	echo "<a" . $linkClass . $dataToggle . " href=\"" . $link . "\">"
		. $iconClass
		. '<span class="sidebar-item-title" >' . Text::_($current->get('title')) . "</span></a>";
}
elseif ($current->get('title') !== null && $current->get('class') !== 'separator')
{
	echo "<a" . $linkClass . $dataToggle . ">"
		. $iconClass
		. '<span class="sidebar-item-title" >' . Text::_($current->get('title')) . "</span></a>";
}
else