The Toad FTP Utility does not work with PuTTY Keys. Is there support for PuTTY Keys?
Toad does not support PuTTY or PuTTY keys at this time. PuTTY keys are not an SSH standard and it is not supported in Toad FTP Utility. PuTTY uses its own unique standard for authentication keys and it is different from the SSH standard.
It is also stated in the Utilities Menu | click FTP | Tips window (to enable / show Tips window, go to Help Menu and click on "Show Tips"):
"Note: Toad does not support PuTTY or PuTTY keys at this time"