我收到以下错误：
ssh -v -i ~/.ssh/shopious.pem ubuntu@54.245.124.178
OpenSSH_5.9p1, OpenSSL 0.9.8r 8 Feb 2011
debug1: Reading configuration data /etc/ssh_config
debug1: /etc/ssh_config line 20: Applying options for *
debug1: Connecting to 54.245.124.178 [54.245.124.178] port 22.
debug1: Connection established.
debug1: identity file /Users/aditya15417/.ssh/shopious.pem type -1
debug1: identity file /Users/aditya15417/.ssh/shopious.pem-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.9p1 Debian-5ubuntu1
debug1: match: OpenSSH_5.9p1 Debian-5ubuntu1 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9
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 66:b7:fd:11:91:1b:bd:a2:b0:58:48:5d:b9:3b:e1:14
debug1: Host '54.245.124.178' is known and matches the RSA host key.
debug1: Found key in /Users/aditya15417/.ssh/known_hosts:12
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: Offering RSA public key: /Users/aditya15417/.ssh/id_rsa
debug1: Authentications that can continue: publickey
debug1: Trying private key: /Users/aditya15417/.ssh/shopious.pem
debug1: read PEM private key done: type RSA
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
该命令曾经有效，但现在不再有效。知道为什么吗？