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NNL-00011:

no server with name "string" exists
Cause: The user issued a SET SERVER request and the current managed Oracle Names server was unable to translate that name into an address. Alternatively, the user issued a control program request to a specific server, and that server's name could not be translated into an address. Both problems are almost always caused by mis-typing the server name.
Action: Re-issue the request with a valid server name.