Server Unexpectedly closed

Not able to connect using putty from Windows.
Just after login,the session is disconnected by putty prompting “Server unexpectedly closed”
I tried below and still issue persists:

  1. Under “Connection” option --> Seconds between keepalives from 0 to 300 (or even 1800 )
  2. Uninstalled the putty tool and downloaded latest version

Not only putty, even the Web console is having the same issue.
Please help!

I have checked from my side there is no issue. Everything works fine.