Amazon EC2 instance is not allowing me to login via SSH from my PC

Amazon EC2 instance is not allowing me to login via SSH from my PC

Remotely, I have been logged in since last night, and it was working fine,
just got timeout, now in the morning i am unable to re-login via SSH to
the same Amazon EC2 box, here is my SSH log:
sun@From-SSH-Client-Ubuntu-Box:~/To-SSH-RHEL6.4$ ssh -v -i amazon.pem
ec2-user@54.22x.x.x
OpenSSH_6.0p1 Debian-3ubuntu1, OpenSSL 1.0.1c 10 May 2012
debug1: Reading configuration data /home/sun/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 54.22x.x.x [54.22x.x.x] port 22.
debug1: Connection established.
debug1: identity file amazon.pem type -1
debug1: identity file amazon.pem-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
debug1: match: OpenSSH_5.3 pat OpenSSH_5*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.0p1 Debian-3ubuntu1
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: Server host key: RSA de:83:e8:bf:51:86:30:89:b9:54:13:52:dc:75:a1:df
debug1: Host '54.22x.x.x' is known and matches the RSA host key.
debug1: Found key in /home/sun/.ssh/known_hosts:39
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,gssapi-keyex,gssapi-with-mic
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure. Minor code may provide more information
Credentials cache file '/tmp/krb5cc_1000' not found
debug1: Unspecified GSS failure. Minor code may provide more information
Credentials cache file '/tmp/krb5cc_1000' not found
debug1: Unspecified GSS failure. Minor code may provide more information
debug1: Unspecified GSS failure. Minor code may provide more information
Credentials cache file '/tmp/krb5cc_1000' not found
debug1: Next authentication method: publickey
debug1: Offering RSA public key: my@gmail.com
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic
debug1: Trying private key: amazon.pem
debug1: read PEM private key done: type RSA
debug1: Authentications that can continue:
publickey,gssapi-keyex,gssapi-with-mic
debug1: No more authentication methods to try.
Permission denied (publickey,gssapi-keyex,gssapi-with-mic).