If there is a remnant of an old Oracle client (perhaps a 32-bit version), remove it via the Control Panel > Programs and Features. Conflicting Oracle Homes are a primary cause of connection failures.
| Installation Type | Use Case | |-------------------|-----------| | Instant Client | Minimal runtime (no SQL Plus, no admin tools) – for most. | | Administrator | Full client with SQL Plus, utilities, ODBC/OLE DB, headers, libraries. Choose this . | | Runtime | No admin tools but includes ODBC/OLE DB. Good for small standalone apps. | Download Oracle Client 11G 64 Bit For Windows 2008 R2
Windows Server 2008 R2 was the first Microsoft server OS to ship exclusively as 64-bit. This means you cannot install a 32-bit Oracle Client and expect native performance or memory addressing above 4GB. The 64-bit client is essential for: If there is a remnant of an old