In message <20010308185226.A16937@quartz.newn.cam.ac.uk>, Patrick Welche writes:
>I therefore changed from ssh 1.2.27 to the in-tree one.
>On one machine all was OK, but the other gives:
>debug: Connecting to john [111.222.333.444] port 22.
>debug: Connection established.
>debug: identity file /home/prlw1/.ssh/identity type 3
>debug: identity file /home/prlw1/.ssh/id_dsa type 3
>ssh_exchange_identification: Connection closed by remote host
>debug: Calling cleanup 0x8057184(0x0)

Your connection is being denied by IP address, typically by the tcp wrapper
code.  This "connection established", "connection closed" is the typical
symptom of that happening.

You will need to look at the settings in your /etc/hosts.allow and
/etc/hosts.deny on the server you are trying to contact, to ensure that 
ssh access is allowed in from the address you are using.

As for the reason that it suddenly changed, I would say that the older
ssh must have been compiled without the tcp wrappers support, and the
newer one is compiled with it turned on.

Hope that helps,

Ewen