Problem with the principal ##MS_PolicyEventProcessingLogin##

I'm trying to send broker messages beteween 2 sql instances on the same server.
I slready succeeded to send and retrieve messages last week. Now I changed the XML validation of the message type (dropping service, contract, message type, contract and recreating them). I'm using a stored procedure that receives the xml message as parameter to send the message. When I call it, I find this in the Profiler :

Broker:Activation
Cannot execute as the database principal because the principal "##MS_PolicyEventProcessingLogin##" does not exist, this type of principal cannot be impersonated, or you do not have permission.

I can see that principal in the sys.database_principals view of the master database (initiator server). But I can't find it on the initiator broker database. Is that normal ?
I also see this message in the profiler : This message could not be delivered because the security context could not be retrieved. But i think it is related to the first message.

Also, there is nothing in both initiator queue and target queue, nor in the sys.transmission_queue view.
Should I recreate the route ? Or the remote service binding ?

How could I solve this security issue ?

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Mike