Sermon images shortcode error

Hello, things were working fine before Christmas but now the following shortcode [sermon_images] produces the error: Warning: Illegal string offset ‘size’ in /home4/coltonsd/maranathacommunity.com/wp-content/plugins/sermon-manager-for-wordpress/includes/class-sm-shortcodes.php on line 493

When I Googled this I found that multiple websites using Sermon Manager were producing the same error message.