Cant approve post/Threads
 

I am trying to approve some old posts and threads and keep getting the following error:

Fatal error: Call to a member function authorize_user_newthread_newpost_notif() on a non-object in /home/forum/people/public_html/includes/class_dm_threadpost.php(879) : eval()'d code on line 43


Could it be that the permissions for that forum location have changes since those posts were created? Could the same error happen because a user was deleted and now is guest?

If so, what are the next steps and what would be the best way to delete those threads?

Thanks.