SSH to a VM fails with "Too many authentication failures"

Symptoms

ssh to a new VM stops with "Received disconnect ... Too many authentication failures".

Cause

The SSH agent offers each of its keys before the one the VM knows. The server allows a few tries (six by default) and closes the connection (observed).

What to do

Name the key and offer only it: ssh -o IdentitiesOnly=yes -i KEY host, or put IdentitiesOnly yes in the host's entry of an SSH config. emupc.py init writes such a config.