More On MySQL Triggers

I have a table `cl35-deal`.`je_PGID`:-

CREATE TABLE `je_parties` (
  `PID` int(4) unsigned NOT NULL AUTO_INCREMENT COMMENT 'ID',
  `PGID` varchar(256) DEFAULT NULL COMMENT 'Global ID',
  `PFullName` varchar(256) DEFAULT NULL COMMENT 'Full Name',
  `PFriendlName` varchar(256) DEFAULT NULL COMMENT 'Name to use for this item',
  PRIMARY KEY (`PID`)
) ENGINE=InnoDB AUTO_INCREMENT=12 DEFAULT CHARSET=latin1;

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On inserting a record I want to trigger an update so that PGID is set to the PID prefixed with the text 'je_'.

I have tried a number of variations on a trigger to do this, eg:-

DELIMITER $$
	CREATE TRIGGER `cl35-deal`.`je_PGID` 
	AFTER INSERT ON `cl35-deal`.`je_parties`
	FOR EACH ROW BEGIN
		UPDATE `cl35-deal`.`je_parties` SET PGID = CONCAT('je_',PID);
	END$$
DELIMITER ;

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I can't get any of them to work most give me an error to do with the SQL syntax all of which I understand. The trigger above (the one I expected to work) gives me an error:-

"Error Code: 1442
Can't update table 'je_parties' in stored function/trigger because it is already used by statement which invoked this stored function/trigger."

I would appreciate help in understanding this message and in getting the trigger to work.