Host-based authentication failure

I'm using host-based ssh authentication between two of my machines at
home.
Using the standard openssh tools, I can ssh freely between them using
any
common accounts.

However, I'm getting auth failures when I try to use Cap across these
machines,
even though the account I'm using can ssh in fine:

  Capistrano::ConnectionError, connection failed for: toad
(Net::SSH::AuthenticationFailed: plu)

I'm played around with the various ssh_options[] options with no luck.

Any ideas? Does it suggest cap is unable to access the server's host
key or something?

Thanks.