SSH to EC2 but get Permission denied (publickey)

Question

I generated the key-pair by EC2-Console, and then store it in ~/.ssh/iForests_ABetADay.pem.
After that, chmod 400 iForests_ABetADay.pem, and ssh -i iForests_ABetADay.pem [email protected] -v.
I did login yesterday, but now the error message I got is:
(Google a lot, but still can not find out a way to solve it...)

OpenSSH_5.6p1, OpenSSL 0.9.8r 8 Feb 2011
debug1: Reading configuration data /etc/ssh_config
debug1: Applying options for *
debug1: Connecting to 46.51.244.48 [46.51.244.48] port 22.
debug1: Connection established.
debug1: identity file iForests_ABetADay.pem type -1
debug1: identity file iForests_ABetADay.pem-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.8p1 Debian-1ubuntu3
debug1: match: OpenSSH_5.8p1 Debian-1ubuntu3 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.6
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client aes128-ctr hmac-md5 none
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP
debug1: SSH2_MSG_KEX_DH_GEX_INIT sent
debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY
debug1: Host '46.51.244.48' is known and matches the RSA host key.
debug1: Found key in /Users/iforests/.ssh/known_hosts:17
debug1: ssh_rsa_verify: signature correct
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Trying private key: iForests_ABetADay.pem
debug1: read PEM private key done: type RSA
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).

Answer 1

The output clearly shows that it's trying wrong key. I suggest that you check

 ~/.ssh/config
 /etc/ssh/ssh_config
 /etc/ssh_config

to see if something forces your client to use iForests_ABetADay.pem. According to log it must be /etc/ssh_config.