Putty: Server unexpectedly closed network connection

When you try to login to a Unix (HP-UX) system, you typed in correct password, but putty tells you "Server unexpectedly closed network connection".
If you configured public key authentication for this account, you see "Authenticating with public key ``key-name`` from agent, and then pop up window tells you "server unexpectedly closed network connection".

If you login as another users, you don't see any log any where (not in /var/adm/syslog/syslog.log, or any other logs).

CAUSE:
The reason of such error is the account is disabled.
If telnet is allowed in your Unix system, try telnet to it and type in the good password, you'll get error message
"Account is disabled - see Account Administrator".  But this is not shown if you login using SSH.

Since lots of place forbid telnet, you may not get a chance to try this.

Solution:
Reactivate the account in SAM, SMH (depends on your release).
After you re activate the user id, you should be able to login as usual in both SSH and telnet.