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NNL-00018:

warning: could not contact default name server
Cause: The control program was unable to contact its default name server during startup. There are a number of possible causes for this error. The control program's SQLNET.ORA file must exist in the correct system-specific location, and must be readable by the control program. The file must contain a names.preferred_servers entry with valid name server addresses. The first server in the preferred-server list must be running, and there must be network connectivity between the control program and that server.
Action: Check to see that all of the above are true. If the control program is still unable to contact its default server, turn on tracing and restart the control program. If the error persists, contact Worldwide Customer Support.