ssh to remote machines using authorized keys

[lists]

Hi all

I have the following situation which I am trying to get around

I have a need to be able to ssh without_password using rsa keys to 
authenticate the ssh session.

I have created and installed the   ~/.ssh/authorized_keys for both a system 
user and for root  on the remote machine and I have changed the 
/etc/ssh/sshd_config accordingly and I have run /etc/rc.d/sshd restart.

I have successfully logged into the remote machine using the rsa keys for 
both the root user and the system user.  The problem I have is that I want 
to log into the remote machine as root from a system user on the main 
machine.  Each time I try I get a password prompt and even if I enter the 
correct root password it gives me "Permission denied 
(publickey,keyboard-interactive,hostbased)"

If I type

user prompt $ ssh user at remote.machine  it works fine
root prompt # ssh root at remote.machine it works fine

but when I type
user prompt  $ ssh root at remote.machine I get  prompted for a password 
followed by the error above, which is "Permission denied 
(publickey,keyboard-interactive,hostbased)"

Can anyone tell me how to get around this?   Is it possible?

Thanks and Regards

Tim