Administrative log was the most informative:
[sqsrvres] CheckQueryProcessorAlive: sqlexecdirect failed
[sqsrvres] printODBCError: sqlstate = HYT00; native error = 0; message = [Microsoft][SQL Server Native Client 10.0]Query timeout expired
[sqsrvres] CheckQueryProcessorAlive: sqlexecdirect failed
[sqsrvres] printODBCError:...