REXEC use in a batch

Well, I have to run a script called by a batch file launched by a command on an AS400 using REXEC service, but it doesn’t run because i need the user/password combination and i can pass only the username. The server on which i have to run the scriptis a win 2k member server.
The command lanched in iterative mode works fine.
Did anyone have met some similar problems?
Thanks