Comment 1 for bug 237297

I figured out the issue: The "The server's host key is not cached in the registry" error is a plink.exe error. Plink.exe must be run previously, so as to add the key to PuTTy's cache:

> plink -v <email address hidden> ls
Looking up host "example.com"
Connecting to 10.10.10.10 port 22
Server version: SSH-2.0-OpenSSH_4.2p1 Debian-7ubuntu3.3
We claim version: SSH-2.0-PuTTY_Release_0.60
Using SSH protocol version 2
Doing Diffie-Hellman group exchange
Doing Diffie-Hellman key exchange with hash SHA-1
The server's host key is not cached in the registry. You
have no guarantee that the server is the computer you
think it is.
The server's rsa2 key fingerprint is:
ssh-rsa 2048 06:e2:36:2b:17:7f:88:29:59:92:bd:e4:1d:15:28:24
If you trust this host, enter "y" to add the key to
PuTTY's cache and carry on connecting.
If you want to carry on connecting just once, without
adding the key to the cache, enter "n".
If you do not trust this host, press Return to abandon the
connection.
Store key in cache? (y/n) y