Task scheduler and sleep; sleeps too soon

I'm having the identical problem to that described here:
http://www.vistax64.com/vista-perfor...-too-soon.html

This was posted some time ago and I'm wondering if there now is a solution.

My experience using Vista Home Premium 32 bit: I have a task that runs
properly when the computer is awake. If it is triggered when the computer is
asleep, the computer wakes, starts the task, but after about 2 minutes the
computer goes to sleep. If I awaken it (by say hitting a key) the task
resumes and finishes properly.

The same issue occurs when my Norton Internet Security virus scan task is
triggered when the computer is asleep. A small number of files are scanned,
then the computer goes to sleep, only to resume at the time I manually awaken
it.

Any help *greatly* appreciated!