Problem using FasterCSV on Import: Can't convert Tempfile to string

Hi,

I'm trying to import a CSV file using fasterCSV and keep getting this
error when trying to import the file.

The parameters are passed from this view:

<% form_for :dump, :url => { :controller => 'mots', :action =>
'mot_csv_import' }, :html => { :multipart => true } do |f| %>
  <p>
    <%= f.label :file, 'Select file to import' %><br />
    <%= f.file_field :file -%>
  </p>
  <p>
    <%= submit_tag "Submit" %>
  </p>
<% end %>

To this action:

  def mot_csv_import
    header_row = true
    row_number = 0
    FasterCSV.foreach(params[:dump][:file]) do |row|
      if not header_row
        Mot.create(
          :vrm => row[4],
          :is_active => 0,
          :is_new => 1)
        row_number += 1
        GC.start if row_number%50 == 0
        header_row = nil
      end
    end
    redirect_to :controller => 'mots', :action => 'index'
  end

Can anyone advise me where I'm going wrong, please?