最近我设置了一个新的EC2实例。第二天我无法通过SSH连接到我的实例。前一天我能够连接和断开连接，我确定我没有做任何更改。以下是SSH调试信息：
ssh -i webserver.pem -v ubuntu@my.elastic.ip
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 my.elastic.ip [my.elastic.ip] port 22.
debug1: Connection established.
debug1: identity file webserver.pem type -1
debug1: identity file webserver.pem-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.9p1 Debian-5ubuntu1.1
debug1: match: OpenSSH_5.9p1 Debian-5ubuntu1.1 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
Connection closed by my.elastic.ip
有没有解决这个问题的方法？还是我需要重新安装我的实例？
PS：我的.pem文件权限设置为600。