I had the same problema, but as described in the manual.pdf, you have to:
You are using an Oracle Instant Client but have not set all required environment variables:
- PATH: Needs to include the Instant Client directory where oci.dll is located
- TNS_ADMIN: Needs to point to the directory where tnsnames.ora is located.
- NLS_LANG: Defines the language, territory, and character set for the client.
Regards