This problem should be fixed in the latest version of Brightbox. The includes/helper-templates.php file is missing the $more variable declaration and a $more = 0; in the blog function.
If you're using version 1.1 or below you can update to version 1.2.1 or replace following code in includes/helper-templates.php:
function blog($element)
{
extract($element['saved_value'][0]);
global $avia_config;
with:
function blog($element)
{
extract($element['saved_value'][0]);
global $avia_config, $more;
And replace:
echo "<div class='template-blog content'>";
get_template_part('includes/loop','index');
with this:
echo "<div class='template-blog content'>";
$more = 0;
get_template_part( 'includes/loop', 'index' );