Connection fails with server unexpectedly closed network connection

The scenario is whenever with any third party software like putty using ssh I try to connect to my unix server through windows machine it fails with message "Server unexpectedly closed network connection"

Solution of The Problem
In my machine I got this problem because of the permission setting of my unix server in the /etc/ssh directory. Someone change the permission of this directory to 777. So it was readable for all and everyone could have access to the secure shell private key. And for this reason ssh could not allow access to the server because of security reason.

The solution of this problem is to change the permission of the /etc/ssh and start the sshd service. To do this,

1)Log on as root user.
$su -root

2)Change permission recursively 600 on /etc/ssh
#chmod -R 600 /etc/ssh

3)Start the ssh daemon.
#service sshd start
or,
#service sshd restart