I try to reboot an windows 2000 computer in an Active Directory domain, with 
"net rpc shutdown" using an domain admin account. the rpc command fails with:

$ net  rpc shutdown -r -I xxx.xxx.xxx.xxx -U administrateur 
Enter administrateur's password:

Shutdown of remote machine failed

result was: WERR_OK

Using -d31 flag, I have some more informations about the probable error:

[2008/11/14 12:28:45, 10] rpc_client/cli_pipe.c:cli_rpc_pipe_open_noauth(2282)
  cli_rpc_pipe_open_noauth: opened pipe \winreg to machine xxx.xxx.xxx.xxx and bound anonymously.
      winreg_InitiateSystemShutdown: struct winreg_InitiateSystemShutdown
          in: struct winreg_InitiateSystemShutdown
              hostname                 : NULL
              message                  : *
                  message: struct initshutdown_String
                      name_len                 : 0x0000 (0)
                      name_size                : 0x0002 (2)
                      name                     : *
                          name: struct initshutdown_String_sub
                              name_size                : 0x00000001 (1)
                              name                     : ''
              timeout                  : 0x00000014 (20)
              force_apps               : 0x00 (0)
              reboot                   : 0x01 (1)
[2008/11/14 12:28:45,  1] librpc/ndr/ndr.c:ndr_push_error(493)
  ndr_push_error(5): Bad character conversion
[2008/11/14 12:28:45, 10] intl/lang_tdb.c:lang_tdb_init(138)
  lang_tdb_init: /usr/lib/samba/fr.msg: Aucun fichier ou dossier de ce type

Shutdown of remote machine failed

result was: DOS code 0xb8fbfb2c
[2008/11/14 12:28:45,  1] utils/net_rpc.c:run_rpc_command(181)
  rpc command function failed! (NT_STATUS_INVALID_PARAMETER)