Warnings on Back-End

Hi,

I’m having this issue on one of our sites:
On the back-end, it has this error:

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘default_password_nag_handler’ not found or invalid function name in /home/nwmedia56/public_html/shannapaxton.com/wp-includes/plugin.php on line 525

Warning: Cannot modify header information – headers already sent by (output started at /home/nwmedia56/public_html/shannapaxton.com/wp-includes/plugin.php:525) in /home/nwmedia56/public_html/shannapaxton.com/wp-includes/option.php on line 820

Warning: Cannot modify header information – headers already sent by (output started at /home/nwmedia56/public_html/shannapaxton.com/wp-includes/plugin.php:525) in /home/nwmedia56/public_html/shannapaxton.com/wp-includes/option.php on line 821

Warning: call_user_func_array() expects parameter 1 to be a valid callback, function ‘default_password_nag’ not found or invalid function name in /home/nwmedia56/public_html/shannapaxton.com/wp-includes/plugin.php on line 525

I have deactivated all of the plugins and themes, and updated all of them, and nothing seems to work. We haven’t made any changes on the site recently. Any ideas?

Thank you!