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I don't understand the error message but ora-12154 is usually caused by an issue with the tnsnames.ora config file.
Try filling in the Service and Port information (instead of leaving it blank) when defining the connection, if recall that should stop it from trying to use the tnsnames file
Click in any blank space at the top of the page and then press the "s" key. This will bring up the search box. Type in 12154:
Also, please read this document: Tableau Server Configuration/DB Connection for Oracle