scp Unable to authenticate. Communication error.

I'm having this issue on one of my AIX box, whenever I try to do scp it asks for user, domain and password and just errors out, scp works fine on other AIX servers.
I already checked the permissions of .sshd and its files, stopped and restarted sshd subsystem.
Also it never asks for user, domain and password on other servers.

Any help would really be appreciated.

####->> ssh -v
OpenSSH_4.3p2, OpenSSL 0.9.7l 28 Sep 2006
AIX version == 5200-10-02-0730

####->> scp -vp /tmp/test venus:/tmp/test.oprx
user: root
domain: xxx.com
password:
Unable to authenticate. Communication error.

Is root allowed to use scp/ssh on this box? Check /etc/ssh/sshd_config

Hi Friend

May be following 3 reson

1) If you are trying to do ssh/scp/sftp from server 1 to server 2 through root login then you need to changed variable in /etc/ssh/sshd_config file i.e. Permitrootlogin=yes
and startsrc -s sshd on server 2
2) password of user on server 2 has got expired for normal user
3) account of user on server 2 has got locked due to some reson

Thanks
Pravin Landge

Yes, root is allowed to ssh/scp/sftp, I can ssh or sftp but no scp

All except the below 2 options are commented out in /etc/ssh/sshd_config

#cat sshd_config | grep PermitRoot
PermitRootLogin yes
# override default of no subsystems
Subsystem sftp /usr/sbin/sftp-server

####->> ssh root@venus date
root@venus's password:
Sat Jan 5 15:40:41 CST 2008

####->> sftp root@venus
Connecting to venus...
root@venus's password:
sftp>

If you do a bare login, is scp on the path for root? There are a couple of different scp protocols and scp uses a copy of scp run by ssh at the far end. If it can't find it, it can't run it.

Porter,
Thanks for ur promt response.
scp is on the path for root, just in case, I even went ahead and added the path /usr/bin/scp and also did tried using various protocols like 1,2,4,6 but still the same thing.