Shutting down a remote computer on Home Network.

I have a small home network with mixed XP and Windows 7, which sits behind a router. There are some wired and wireless connections. One of the wired XPs (ZZ say) controls a printer which is shared. The PC has no other function.
At present ZZ uses autologon when switched on and this works well - all network PCs can use the printer. I want to be able to turn it off remotely, but when I use the command "shutdown -s -m \\ZZ -t 10" I get the response "The network path was not found". I can ping it using its name or IP address and it appears in "My Network places". I read somewhere that winsock might be damaged. I used the MS Winsock2 Fixit but that made no difference.
I would be grateful for any advice or suggestions.