This is my solution to a problem I find posted many times over the past few years, many of the posts marked "solved" or otherwise locked even though only in one instance did I see a real solution listed (other than uninstalling Norton).
I recently "automatically" updated to 360. I am using Windows 7. I had the same problem as many have had with various versions of Norton: the Windows native screensaver was being interrupted by Norton idle tasks, and when the screensaver shut off, the idle tasks then aborted.
I went to Norton's Settings > Administrative Settings and TURNED OFF "Norton Task Notification"
This ended my problem. Screensaver now works, and so do the idle tasks.