I am using SQL Service Broker and send messages from a trigger.
Now I have a problem: during the sending I receive:

An exception occurred while enqueueing a message in the target queue.
Error: 33019, State: 1. Cannot create implicit user for the special
login ‘sa’.

My queue is created as

ALTER QUEUE [sales].[QOrders] WITH STATUS = ON , RETENTION = OFF , ACTIVATION (  STATUS = OFF , PROCEDURE_NAME = [sales].[orders_dequeue] , 
MAX_QUEUE_READERS = 3 , EXECUTE AS  N'dbo'), POISON_MESSAGE_HANDLING (STATUS = OFF) 

I have tried to change: EXECUTE AS OWNER, EXECUTE AS SELF – the same error.
How to fix it?