To copy a file to a remote workstation, you must ensure that the receiving workstation is configured for such a task.
If you copying a file to the root directory, ensure that the /.rhosts file is properly populated. Bear in mind that the login directory for the root account could be set to something else other than /, so check your /etc/passwd file to verify. Suppose I wanted to copy /etc/default/login to another workstation.
On remote workstation:
#vi /.rhosts
remote_workstation root
:wq! (saves and quits)
On local workstation:
#rcp -p /etc/default/login remote_workstation:/etc/default