Hi!
Seems as if your provider updated your PHP version, and your current s9y version is not compatible with the upgraded PHP.
So the best thing would be for you to upgrade to Serendipity 1.1 (proceed using the upgrade procedure in our FAQ on
www.s9y.org).
Another thing would be to edit the metnioned include/compact.inc.php file and remove the block where it checks for "input_na,e_to_filter".
Best regards,
Garvin