The exact error in the SQL Server log is:
The activated proc [dbo].[QSVThreatAssesmentProcessor] running on queue [Errors].[dbo[.[QSVInputQueue] output the following: 'Login failed for user 'xxxxxx'.'
The procedure is being activated and executed but evidently reports an error somewhere... The user 'xxxxxx' is the EXECUTE AS user for the activation procedure.
When I log in to SQL Server as that user and execute the activation procedure from a session it executes perfectly and does what it is supposed to do. The frustrating thing about this is that it was working and appears to have stopped when I made the database 'trustworthy' . Maybe I should set trustworthy off and try it again, but we will be bouncing the server tomorrow morning so I'd like to see if that helps.
The probability of survival is inversely proportional to the angle of arrival.