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- If you are using local naming (TNSNAMES.ORA file):

- Make sure that "TNSNAMES" is listed as one of the values of the NAMES.DIRECTORY_PATH parameter in the Oracle Net profile (SQLNET.ORA)

- Verify that a TNSNAMES.ORA file exists and is in the proper directory and is accessible.

- Check that the net service name used as the connect identifier exists in the TNSNAMES.ORA file.

- Make sure there are no syntax errors anywhere in the TNSNAMES.ORA file. Look for unmatched parentheses or stray characters. Errors in a TNSNAMES.ORA file may make it unusable.

- If you are using directory naming:

- Verify that "LDAP" is listed as one of the values of the NAMES.DIRETORY_PATH parameter in the Oracle Net profile (SQLNET.ORA).

- Verify that the LDAP directory server is up and that it is accessible.

- Verify that the net service name or database name used as the connect identifier is configured in the directory.

- Verify that the default context being used is correct by specifying a fully qualified net service name or a full LDAP DN as the connect identifier

- If you are using easy connect naming:

- Verify that "EZCONNECT" is listed as one of the values of the NAMES.DIRETORY_PATH parameter in the Oracle Net profile (SQLNET.ORA).

- Make sure the host, port and service name specified are correct.

- Try enclosing the connect identifier in quote marks. See the Oracle Net Services Administrators Guide or the Oracle operating system specific guide for more information on naming.