Full description of error:
Warning: Missing argument 2 for wp_kses(), called in ..wp-content/plugins/really-simple-gallery-widget/really-simple-gallery-widget.php on line 57 and defined in ../wp-includes/kses.php on line 476
Had similar error with another plugin which had to do with that plugin's improper use of $wpdb->prepare();
Not sure if this is same problem but the error is worded pretty much identically
Please post the edit for the fix here so I can make proper corrections in advance of next plugin update. I'm not sure where to make an edit to fix the problem.
BTW, I'm using WP 3.6 and a child theme of Twenty Eleven (latest update), and the latest plugin (v 1.3)