I manage many WordPress websites and sometimes ( it’s like almost never) after an update (theme, plugin, wp..) I get strange errors or warnings at the top of my dashboard, and on the Front-end.
Usually it is nothing to worry about. But the real problem starts when the notifications about the error/warning just don’t want to go away!
In this case scenario you have to edit your WP-CONFIG file.
Put this in it:
ini_set('display_errors','Off');
ini_set('error_reporting', E_ALL );
define('WP_DEBUG', false);
define('WP_DEBUG_DISPLAY', false);
Save the changes you made and Voila > No more PHP nags.
Enjoy!
(ps. If you already have define('WP_DEBUG', false);
then just replace it with the code I gave you)