When setting up a new Database Agent, some MS SQLServer instances are set as named instances so ports are set dynamically. Per the documentation you would normally set the DB name and port number like so: dc2uc4:1433
However, with a dynamic port this doesn't work.
?Named instances can be handled for the server name like the following:
The SQL Server browser service must be running as well.
You can also specify other jdbc properties in the server field of the sql job.