Can't connect to one server from a particular LAN

I can't ssh to a server from any machine on one particular LAN - here's
the debug:

OpenSSH_4.2p1 Debian-7ubuntu3.1, OpenSSL 0.9.8a 11 Oct 2005
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to [] port 22.
debug1: Connection established.
debug1: identity file /home/mark/.ssh/identity type -1
debug1: identity file /home/mark/.ssh/id_rsa type -1
debug1: identity file /home/mark/.ssh/id_dsa type -1
ssh_exchange_identification: read: Connection reset by peer

I can connect to this server port 22 from a different LAN; I can also
telnet to the server from this LAN.
The debug is from an attempt from an Ubuntu box; I normally attempt to
connect from XP using putty, and get a 'Network error: software caused
connection abort' error.

All suggestions gratefully received...


Relevant Pages