[Setup] Error buildout - add products

[Tk]

Hi, 
I'm new user, so i installed Plone 4 and i would like to add products like
Products.PloneFormGen but when
i uncomment Products.PloneFormGen on my buildout.cfg and re-run buildout,
this error appear :
Uninstalling instance.
Updating productdistros.
Installing instance.
Getting distribution for 'Products.PloneFormGen'.
While:
  Installing instance.
  Getting distribution for 'Products.PloneFormGen'.
Error: Couldn't find a distribution for 'Products.PloneFormGen'.

I don't know what is missing. Please help me
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