Connecting to a RAC database with TAF using an 11g client on Toad 10.1.1.8 gave the following error:
"ORA-01017: invalid username/password."
The 11g case sensitive feature is turned off. That is ALTER SYSTEM SET SEC_CASE_SENSITIVE_LOGON = FALSE.
Use a 10g client with Toad 10.1.1.8 to connect to your RAC with TAF.
Enhancement request has been submitted to Development for consideration in a future release of Toad for Oracle.