[Samba] net rpc shutdown not working

[zorg]

hi
jI'm trying to shutdown some windows XP clients with
net rpc shutdown -S <name>  -U administrator%password
but all i get is this error
[2004/11/26 10:44:32, 0] utils/net_rpc.c:rpc_shutdown_internals(4113)
Shutdown of remote machine failed!

I'm using Version 3.0.8-Debian
and le client are using winXP SP2 (the firewall is not activated)

if someone can help

thank

cyril