Symptom 1The SQL Server Agent log file displays a message that resembles the following:
SQLServerAgent cannot start
2016-08-06 14:54:46 - !  SQLServer Error:
65535, SQL Server Network Interfaces: Error Locating Server/Instance Specified
[xFFFFFFFF]. [SQLSTATE 08001]
2016-08-06 14:54:46 - !  ODBC Error: 0,
Login timeout expired [SQLSTATE HYT00]
2016-08-06 14:54:46 - ! 
SQLServer Error: 65535, A network-related or instance-specific error has
occurred while establishing a connection to SQL Server. Server is not found or
not accessible. Check if instance name is correct and if SQL Server is
configured to allow remote connections. For more information see SQL Server
Books Online. [SQLSTATE 08001]
When you try to read the SQL Server error log, the attempt fails, and an error that resembles the following is returned:
An exception occurred while executing a Transact-SQL statement or batch. (Microsoft.SqlServer.ConnectionInfo)
Failed to open loopback connection. Please see event log for more information.
Msg 22004, Level 16, State 1, Line 0
Error log location not found.
Certain maintenance plans or SQL Agent jobs, such as a maintenance cleanup task to delete old backup or report files "silently" fail. In the case of the cleanup task, the files that you expect to be deleted are not deleted when the corresponding job is run, and no error is written to the SQL Server log. Executing sp_readerrorlog would result in Symptom 2.