Under Ruby 1.9, princely fails to generate a pdf with the following error:

ArgumentError (invalid byte sequence in UTF-8)

The solution seems to be forcing binary encoding of the data you pass into the send_data method used by princely:

def make_and_send_pdf(pdf_name, options = {})
  send_data(
    make_pdf(options).force_encoding('BINARY'),
    :filename => pdf_name + ".pdf",
    :type => 'application/pdf'
  ) 
end

I’m not sure whether this is the best solution but it worked. Another solution used ASCII-8BIT instead of BINARY.

Specific versions: Ruby 1.9.2, Rails 2.3.10, Prince 6, Princely 1.2.5