Can't open an xcl workbook on a mac with rb-appscript

I get an errror when I try to open a workbook

require “appscript”
include Appscript

excel=app(‘Microsoft Excel’)
excel.activate
workbook=excel.open_workbook(:workbook_filename=>“Macintosh
HD::Files::Data.xlsx”)

Does any one here have any ideas as to what I can do? I am out of ideas

/opt/local/lib/ruby1.9/site_ruby/1.9.1/appscript.rb:467:in block in _send_command': Unknown keyword parameter: :workbook_filename (ArgumentError) from /opt/local/lib/ruby1.9/site_ruby/1.9.1/appscript.rb:464:ineach’
from /opt/local/lib/ruby1.9/site_ruby/1.9.1/appscript.rb:464:in
_send_command' from /opt/local/lib/ruby1.9/site_ruby/1.9.1/appscript.rb:643:inmethod_missing’
from test.rb:6:in `’