Trigger generating Error On INSERT

[IGGt .]

I have a trigger I have devised that is designed so that when a row is INSERTED into a table, if it matches, then the trigger adds a second row.

But it doesn't work, I keep getting "Can't update table 'tablename' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.

The trigger is:

delimiter //
CREATE TRIGGER triggertest
AFTER INSERT
ON tablename
FOR EACH ROW
BEGIN
IF NEW.state = 4
AND NEW.Task = 300
THEN
INSERT IGNORE INTO tablename
(State, task, Data)
VALUES (5,300,'stuff');
END IF;
END
;
//

and the query is:
INSERT INTO tablename
VALUES (4,300,'data');

Therefore this query should result in two rows being added, but instead I get the error message.