Problem with trigger function

Hi,
I wrote the trigger function below and when trying to execute it, I
get the following error:

15:00:42 [CREATE - 0 row(s), 0.000 secs] [Error Code: 0, SQL
State: 42601] ERROR: syntax error at or near "INSERT"

I am using DBVisualizer's "SQL Commander" window, not the "create
funciton" option. I know the SQL is correct - I can execute it just
by itself. The problem is somewhere in the
syntax for a postgres trigger function. Any input on what the problem
might be would be just fabulous!

Many thanks,
Mira

CREATE OR REPLACE FUNCTION audit_sequence_update() RETURNS trigger AS '
BEGIN
IF tg_op = ''INSERT'' THEN
INSERT INTO audit_sequence_update(operation, "day",
owner_uid, "sequence")
VALUES
('INSERT', NEW."day", NEW.owner_uid, NEW."sequence");
ELSE
INSERT INTO audit_sequence_update(operation, "day",
owner_uid, "sequence")
SELECT
'UPDATE', "day", owner_uid, "sequence"
FROM sequence where isdid=NEW.isdid;
END IF;
RETURN NEW;
END
' LANGUAGE plpgsql;