Problem:  Linux ssh sessions immediately timing out
Potential Solution: edit /etc/ssh/sshd_config, make sure the following 
values exist and make sure the following commented (#'d) lines are commented 
in this file, then restart the sshd process (e.g., "service sshd restart")

# X11UseLocalhost yes
# PrintMotd yes
# PrintLastLog yes
TCPKeepAlive yes
# UseLogin no
UsePrivilegeSeparation no
# PermitUserEnvironment no
# Compression yes
ClientAliveInterval 300
ClientAliveCountMax 3
# UseDNS yes
# PidFile /var/run/
MaxStartups 175
# ShowPatchLevel no

NOTE: This is an aid for ONLY the most desperate situations.  The numeric 
values shown are only done so as an attempt to get ssh running reasonably 
and should be fine tuned by your system manager.  Please consult your system 
manager and/or check out the man pages by typing "man 5 sshd_config" for more 
info if this is a non-urgent situation.