Activating screen saver from AppleScript in Mountain Lion
Solution 1:
That is a nice way of starting a random screen saver. If, however, you'd simply like to start the active screen saver, you can use this in Mountain Lion:
tell application "System Events"
start current screen saver
end tell
Solution 2:
This works in ML:
tell application "System Events"
set ss to screen saver "Random"
start ss
end tell
"Random" can be replaced with your choice, "Flurry" or "Shell" and so on.
Source Disclosure: http://hintsforums.macworld.com/showthread.php?t=111478
Solution 3:
tell application "ScreenSaverEngine" to run