My error log is being inunddo with the error: call_user_func_array() expects par

My error log is being inunddo with the error: PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, class ‘FatPandaFacebookComments’ does not have a method ‘wp_head’ in /home/#####/public_html/wp-includes/plugin.php on line 505

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