APEX

I get an error like that:

ORA-04091: table TRACKER.REQUESTS is mutating, trigger/function may not see it
ORA-06512: at "TRACKER.REQUESTS_EMAIL", line 4
ORA-06512: at "TRACKER.REQUESTS_EMAIL", line 16
ORA-04088: error during execution of trigger

My trigger code is:

create or replace trigger "REQUESTS_EMAIL"
	after update of status
	on requests
	referencing new as new old as old
	for each row
declare
	cursor mail_overdue
	is
		select	username, assigned_email, form_name, request_id
		  from	assigned, form_type, requests
		where       assigned.assigned_id = form_type.assigned_id
				and form_type.form_id = requests.related_form_id(+)
				and :new.status = 'Overdue';

	request_id		number;
	v_request_id	number;
	v_mail		varchar2 (250);
	v_user		varchar2 (250);
	v_form		varchar2 (250);
begin
	for emp_rec in mail_overdue
	loop
		v_request_id := emp_rec.request_id;
		v_mail := emp_rec.assigned_email;
		v_user := emp_rec.username;
		v_form := emp_rec.form_name;

		apex_mail.send (
			p_to		=> v_mail,
			p_from	=> v_mail,
			p_body	=> 'You have an overdue request in Request Tracker. '
						  || CHR (10)
						  || ' Request: '
						  || v_request_id
						  || CHR (10)
						  || ' Type: '
						  || v_form
						  || CHR (10)
						  || ' Login: '
						  || v_user
						  || CHR (10)
						  || ' Pass: '
						  || '******',
			p_subj	=> 'Overdue Request'
		);
	end loop;
end;
/

The trigger compiles with no errors. The error I get when trying to update the table!

I suspect a problem is in the trigger's code?

I absolutely need to make a trigger as "after" update.

Thank you for consideration!