issue in fetching long list of geolocations in rails

The following script works fine for me but after fetching some records (generally 100 records) it failed and give me error:--

Invalid JSON string

and sometimes after fetching some 500 records it stop fetching coordinates. I need to fecth some 18000 coordinates any suggestions??

 task :populate_geolocations_reverse => :environment do
  AdvocateDetail.order("id DESC").all.each do |advocate|
  p advocate.id
  if advocate.latitude.nil? or advocate.latitude==0 or advocate.latitude=="0"
     p "fetching geolocations...:-( "
     a = Geocoder.fetch_coordinates(advocate.address)
     unless a.nil?
       p "got geo开发者_如何学Golocations... :-) "
       advocate.latitude=a[0]
       advocate.longitude=a[1]
       p "saving geolocations...:-P "
     advocate.save(false)
  end
else
   p " already have geolocations for this Jumped....:-)"
end
end
p "transformation done... "

end

Please remember that google has its limit to serve your requests. It is around 1000 unique requests per day and 1 per second. As I know Geokit uses more services than google itself, but it still may be limited. Take a closer look on that.