no thumnails


I have installed upload_fu(and its requiriments) The problem i got is that the upload works fine, but it does fails creating the thmnails. The app does not trhougth any error in the log file nor the console, so i do not know what coul be the problem.

I open up irb i put these 2 commands:

require 'rubygems'
require 'image_science'

both of them response "true" . An idea?