I'm Using local naming (TNSNAMES.ORA file):
"TNSNAMES" is listed as one of the values of the NAMES.DIRECTORY_PATH parameter in the Oracle Net profile (SQLNET.ORA)
TNSNAMES.ORA file exists and is in the proper directory and is accessible.
The net service name used as the connect identifier exists in the TNSNAMES.ORA file.
I think there are no syntax errors anywhere in the TNSNAMES.ORA file.