OK, wganesh, this really is an issue connected with the fact that TDM is a 32bit app while your Toad and Oracle Client are 64bit. It’s not possible to use a 32bit client with 64bit Toad unfortunately, so currently there is no way to make this combination work. There are already 3 change requests covering this issue, 103280, 109387 and 110075, and the whole issue should be fixed in the next or after next release. Follow Release Notes to see the CR fixed.
Either use TOAD DIRECT connection, or create a new connection in Toad Data Modeler (TCP or Native with use of TNS, if you do not want to/cannot use direct connection).