I've recently fixed a simple problem and I would like to share it with you.
We have one huge package on the notification server which recently started to time out before update distribution points finished.
The solution is simple!
You need to increase the http timeout, which is by default set to 10 minutes.
Locate C:\Program Files\Altiris\Notification Server\Web\web.config and find a line which contains "httpRuntime executionTimeout". Change the value from 600 (in seconds) to something larger like 900.
Restart the Symantec and IIS services or just simply reboot and voila :)
This worked for me.