MYSQL trigger You can't specify target table 'XXX' for update in FROM clause

[silversubey]

I am trying to convert mssql triggers to mysql. I am very new to Mysql and would like some help with my code. My queries work but there has to be a more efficient way to write them. I would greatly appreciate any help. the following is a trigger that works until I add the last update statement. thanks for the help.
Mysql 5

delimiter //
Create TRIGGER User_Rating_Avg After Insert on bksite.Ratings
FOR EACH ROW
BEGIN
UPDATE bksite.bookkeepers SET User_Cost_Avg=
(SELECT SUM(cost)/(SELECT count(*) FROM bksite.ratings where bkid = new.bkid) from ratings where bkid = new.bkid)
where bkid = new.bkid;
 
UPDATE bksite.bookkeepers SET User_Knowledge_Avg=
(SELECT SUM(knowledge)/(SELECT count(*) FROM bksite.ratings where bkid = new.bkid) from ratings where bkid = new.bkid)
where bkid = new.bkid;
 
UPDATE bksite.bookkeepers SET User_Speed_Avg=
(SELECT SUM(speed)/(SELECT count(*) FROM bksite.ratings where bkid = new.bkid) from ratings where bkid = new.bkid)
where bkid = new.bkid;
 
UPDATE bksite.bookkeepers SET User_Accuracy_Avg=
(SELECT SUM(accuracy)/(SELECT count(*) FROM bksite.ratings where bkid = new.bkid) from ratings where bkid = new.bkid)
where bkid = new.bkid;
END;
//
 

the trigger fails when i insert this last bit. the error is You can't specify target table 'XXX' for update in FROM clause

UPDATE bksite.bookkeepers SET User_Avg_Total=
(SELECT (User_knowledge_avg + User_Cost_Avg + User_Speed_Avg + User_Accuracy_Avg)/4 FROM Bookkeepers
where bkid =new.bkid);