Considering this is probably a production server if you want to hide this, you should be doing custom error reporting as is. In php.ini set
display_errors = Off
log_errors = On
This way, errors aren't pushed to the screen, but are instead, logged in a file
The message itself is a PHP error message, therefor couldn't be changed by IIS or Apache. If you could configure it, it would need to be done in the PHP files. Though, this may require a source hack.