SSH times out - "Server unexpectedly closed network connection"

[Robert G.]

SSH doesn't appear to be working on my remote server. I can connect 
fine, and am prompted with "login as: " with Putty, but when I enter my 
username it sits and hangs there for about a minute before a message 
comes up that says "Server unexpectedly closed network connection". SSH 
was working fine this morning around 11am. I just got back and now it's 
hanging. The only changes to the /etc/ssh/sshd_config that I made were 
to add my one user account. I rebooted and it worked fine this morning, 
so I don't know what the problem is now as I haven't touched it.

Any ideas?

-- 
Robert G.