problem with keyword 'old'

I am ussing Postgresql v. 6.3 in a RedHat Linux system. I try to create a
rule to log the deletes on table 'filter' ussing the following:
CREATE RULE log_delete_filter AS  ON DELETE TO filter DO INSERT INTO log_activity (mod_table, mod_record, mod_type)
VALUES('filter', old.did, 'D');
 
The atributes of tables are:   filter (did int4, text text)   log_activity (mod_table char(20), mod_rec int4, mod_type
char(1))
 
I have the following result:   ERROR:  old: Table does not exist.and the rule is not created.
I tested a same rule on INSERT with the keyword new.did and is working
perfect.Also I tested the commands:SELECT new.did;> ERROR:  NEW used in non-rule querySELECT current.did;>ERROR:
CURRENTused in non-rule querySELECT old.did;>ERROR:  old: Table does not exist.
 
What is going on? Do you have any idea why does system not undestand
keyword 'old'?

Sincerely,Basilis Kladis <bkladis@knowledge.gr>

Βασίλης Κλάδης
Language Engineering Dept.
KNOWLEDGE S.A.