onAppear / onVanish not working

Hello, I've been using Sikuli for a couple of days (I'm not a python programmer) but I cannot make onAppear or onVanish to work.

I've read there is a problem with observe(background = True) on Windows 7 32-bit wich I am currently using.

This is the script:

def feed(onAppear):
 pass
 click("image-path")
 wait(1)
 hover("image-path")
 wait(2)
 click("image-path")
 return

onVanish("image-path", feed)
observe(background= True)

while (1):
  doubleClick("image-path")
  wait(2)
  type ("r",KEY_ALT)
  wait(30)

The script performs the while bucle perfectly, however observe won't trigger. onVanish searchs for a image of a decreasing bar. I've tested it and Sikuli finds correctly when the bar has vanished, oddly enough feed function won't work.

Thanks