Im getting an Array / Warning Error HELP please

Ok guys i would really appreitiate it if you could help me out. Im getting this error at the top of my homepage everytime and im a real noobie so i need a step by step instructions please i searched everywhere on google and there was no luck:/ heres the warning:

Warning: call_user_func_array() [function.call-user-func-array]: First argument is expected to be a valid callback, ‘_close_comments_for_old_posts’ was given in /home/factinco/public_html/wp-includes/plugin.php on line 163

Heres my site: https://factincorporated.com

I also need to make this a business site and its not working for me any ideas or suggestions i would really appriciate as soon as possible thanks!!