Here's some notes I keep to help me. Though I wrote it for Tableau Server it still applies to the desktop. This is as far as I can help.
Oracle has ALWAYS been a PITA to deal with
Oracle Connection.doc 72.0 KB
One line in your document resolved the issue,
and manually create the directory C:\Oracle_Client\network\admin
Initially I used the original TNSNames.ora document in the default path: C:\Oracle\product\11.2.0\client_1\network\admin, and even configured the system environment to that location and it didn't work.
After manually creating the directory as mentioned above and configured the system environment to it, it worked. WEIRD.