Paperclip - undefined method `match' for nil:NilClass
===

I'm new to rails, and ruby. I'm creating a simple application where I can upload a photo. I have the paperclip gem installed and I'm trying to configure it within my model to specify a thumbnail size like so:

    has_attached_file :photo, 
      	:styles => {:thumb => '120x120>', :large => '640x480>' },
      	:default_style => :thumb,
        :url => "/system/photos/:basename.:extension",
        :path => ":rails_root/public/system/photos/:basename.:extension"

However, I keep receiving the error:

    undefined method `match' for nil:NilClass

When I remove the :styles parameter, everything works as expected.

Can anybody shed some light and point me in the right direction? 

Thanks