You say you’re using Toad for Oracle 10g – there is no such thing. So I’m guessing you’re running Toad 10.0, 10.1 or 10.5 – all of which are 32-bit only apps
and require 32-bit Oracle client (read the 1st blog below). Toad does not offer a 64-bit version – which you must download specifically – until Toad 11.6.