CSV Export error

Hi guys, When I export data into a .csv file, it works perfectly. when
I push the code to heroku, I get the following error:
ActionView::Template::Error (can't convert Hash into String):

My helper to generate the csv is:
def generate_csv
   csv_str = CSV.generate(:col_sep => ",") do |csv|
      Entrant.find(:all).each do |entrant|
        csv << [entrant.firstname, entrant.lastname, entrant.email,
entrant.entrydate]
      end
    end
  end

Is there any reason why I would get this error?

Thanks in advance for your help.

Hi guys, When I export data into a .csv file, it works perfectly. when
I push the code to heroku, I get the following error:
ActionView::Template::Error (can't convert Hash into String):

Are you running the same ruby version locally and in production ? This looks like it might be a ruby 1.8 vs 1.9 thing (the csv library was rewritten for 1.9)

Fred