[ec2] AWS problem or bad Canonical ami?

[Peter Wolanin]

Following the instructions here:
https://help.ubuntu.com/community/EC2StartersGuide  I consistently am
unable to authenticate to a freshly launched 8.04 image using an
existing ssh key, even though the ssh key fingerprint matches.  I
don't see the same problem with other amis, so I'm tending to think
this is an issue with specific to how these amis run?

$ ec2-describe-instances i-e3fad88a
RESERVATION	r-1d601e74	831208250803	fields_dev
INSTANCE	i-e3fad88a	ami-5d59be34	ec2-174-129-152-156.compute-1.amazonaws.com	domU-12-31-39-04-51-12.compute-1.internal	running	default	0		m1.small	2009-06-28T15:29:20+0000	us-east-1b	aki-6e709707	ari-6c709705		monitoring-disabled

$ ssh -i /Volumes/acquia/ssh/id_acquia_default
ubuntu at ec2-174-129-152-156.compute-1.amazonaws.com
The authenticity of host 'ec2-174-129-152-156.compute-1.amazonaws.com
(174.129.152.156)' can't be established.
RSA key fingerprint is ca:48:6a:e3:f3:08:20:58:d2:9e:f7:3d:32:b2:1a:1c.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added
'ec2-174-129-152-156.compute-1.amazonaws.com,174.129.152.156' (RSA) to
the list of known hosts.
Permission denied (publickey).

$ ssh -i /Volumes/acquia/ssh/id_acquia_default
root at ec2-174-129-152-156.compute-1.amazonaws.com
Permission denied (publickey).

$ ec2-describe-keypairs default
KEYPAIR	default	1d:41:9e:ec:aa:6e:ce:40:91:30:19:f1:24:15:77:9d:50:bd:db:96

$ ec2fp /Volumes/acquia/ssh/id_acquia_default
1d:41:9e:ec:aa:6e:ce:40:91:30:19:f1:24:15:77:9d:50:bd:db:96