Newer versions of OpenSSH have deprecated small key sizes for security reasons. We still have some older equipment that uses these types of keys that we need to access. You can work around this with:

ssh -o RSAMinSize=1024 user@domain.com

Normally I use SSH keys (with a password) to login to remote machines. Today I needed to force SSH to use a password to verify a change. Here is the command:

ssh -o PubkeyAuthentication=no user@server.domain.com