Sorry I am a bit of a novice. I can't find the code being referred to
please confirm whether you are using share this widget or not
and why not post a test user login for someone experienced to check the referred issue ?
I am not using a share this plugin.
Sorry, log in
Testuser
12345
basically report.php file appears to be missing or not accessible.
run file verification tool available at tools & maintenance section of admin panel to find missing / changed files.
ignore files reported from install folder & its subfolders. you have to replace reported files from MyBB source
files pack of your forum's version. (as you are using Google SEO plugin , do not replace ~/inc/functions.php file)