PC wakes for backup but goes back to sleep before finished

Hi,

I have just installed a WHS which I want to use to backup 2 PCs both running Vista (1x32bit, 1x64bit). Doing manual backups all works fine but when it comes to waking the pcs to do the automatic backup they both go back to sleep with in 2 mins of waking up and the backup hasn't even started in that time or if it has gets interrupted.

I did test setting a scheduled job that forces the system to wake up and found it does the same thing, wakes for the job then with in 2 mins goes back to sleep.

Is there a way to make Vista stay awake when woken by RTC event until it's normal duration before sleeping has passed?

Only work around I can think of is running a task that wakes the PC and changes the power options to always on, then run another task 30mins later to put it back. Which should work but hoping for a nicer fix then this.

Thanks
Gori