Did you have enable WOL ?
Task: Tickle Client (see HOWTO60829)
This task uses a "proxy agent" as configured in the Targeted Agent Settings to send a broadcast packet to the sleeping computer. It also ships with the main SMP product for free. It works by first finding a computer on the same "last known" subnet as the target, sending a packet to the agent on this subnet, which then sends out a broadcast packet with a target of the known MAC for the client you are trying to wake up. If there are no active or responding systems on that subnet, it will fail. And, because we don't know in "real time" which agents are active (vs the first method above that uses Task to know about current active status), it can be a bit of a hit and miss
http://www.symantec.com/business/support/index?page=content&id=HOWTO60817