Ongoing error messages

[CalebMurdock]

I am getting error messages when I make posts. They always happen when I am starting a new thread, and sometimes they happen when I am posting a comment on a thread that already exist. They look like a blank page with something like this at the top (always in large letters):

[phpBB Debug] PHP Warning: in file [ROOT]/includes/functions_messenger.php on line 506: count(): Parameter must be an array or an object that implements Countable
[phpBB Debug] PHP Warning: in file [ROOT]/includes/functions.php on line 1836: Cannot modify header information - headers already sent by (output started at [ROOT]/includes/functions.php:3268)

I haven't made much of an issue about it up to now because the post always appears on the board. It's just annoying.

Can anyone help?