PHP Error 68

Hi there, I just found a “notice” about a PHP error and was wondering if you can help resolve it. This is what I see: wp-content/plugins/azindex/az-index-admin.php:68. Here is the actual screenshot of the full error detail: https://strongdisciple.com/wp-content/uploads/phperror68.png

Any advice would be appreciated.

The page I need help with: [log in to see the link]