Openssh in batch from Windows with public key

Hello, I have a problem with a openssh client running on a Windows 2003 server; 
the client has to connect to a ssh server running on a Linux Red Hat Enterprise 
4, using public key authentication.
I've run through all the required steps, and everything works fine when I 
connect interactively (logon to the Windows 2003 server, and running this line 
from a dos prompt to execute a command on the remote server : "ssh user@server 
command".
The problem arises when I want to do the same thing through a batch run by a 
scheduler; I'm using a Unicenter scheduler, but the problem is the same if I 
use Windows task scheduler. The batch job hangs, and I cannot obtain any kind 
of log; in my opinion, it cannot find the public key of the user. I tried with 
the -i option, but no result; anyone can help me ?
Thanks     Bruno