I am trying to set up a linked server from SQL Server Production to one of our Oracle instances but experiencing this error : 
The test connection in ODBC succeeds, but it fails on SQL Server side. I have checked the following things:
OLEDB provider is installed
OLEDB bit matches the bit of SQL
OLEDB is registered
Linked server properties is the last option to be able to login in using username and password
Oracle provider has Allow In process checked
Oracle ports are opened
The right version client is installed
Are there anything else I should check further to resolve this error? Please provide me suggestions if you have experienced this before and what has worked for you. TIA