Flash by default does not understand parameters like & (&)
there fore when you send parameters to your flash based apps you need to encode them so that flash would not strip it off thinking that the query has finished.
This is just a small helper that does it.
def flash_friendly_url_for(options={})
url = url_for(options)
url.gsub!(/&/,'%26')
url
end
<param name="FlashVars"
value="&dataURL=<%= flash_friendly_url_for(
:action => "show_graph",
:start_date => params[:start_date],
:end_date => params[:end_date],
)%>&chartWidth=800&chartHeight=400" />
Follow this article for more information on Flash URL encoding