AppleScript switch spaces

I can press control-2 to go to space 2, for example. so, i am coding it in AppleScript.

1. In System Preferences (Exposé & Spaces), set "Enable Spaces"
2. In System Preferences (Universal Access), set "Enable access for assistive devices"
3. Go to Space 1 if you are not there already
4. In AppleScript Editor, paste the following code
   • tell application "System Events"
   • keystroke "2" using {control down}
   • end tell
5. Click button "Run"

However, the script does not go to space 2 but just beeps. why?