link_to_remote not working

This was a link_to_remote in rails 2. Now i changed it to link_to with
remote=>true
But it still does not work
I have added this in my gemfile and done bundle install
gem 'prototype_legacy_helper', '0.0.0', :git =>
'git://github.com/rails/prototype_legacy_helper.git'

<%= link_to( "replace" ,:update => 'doc_' + doc.id.to_s, :url => {
:action => :replace , :id => @docset, :old_id => doc.id, :new_id =>
new_doc.id },:remote=>true) %>

This was a link_to_remote in rails 2. Now i changed it to link_to with
remote=>true
But it still does not work
I have added this in my gemfile and done bundle install
gem 'prototype_legacy_helper', '0.0.0', :git =>
'git://github.com/rails/prototype_legacy_helper.git'

<%= link_to( "replace" ,:update => 'doc_' + doc.id.to_s, :url => {
:action => :replace , :id => @docset, :old_id => doc.id, :new_id =>
new_doc.id },:remote=>true) %>

The first thing you need to do is to work out which bit is not
working. Is the link_to not generating the correct html? Are the
wrong parameters being posted? Is the controller action not working
correctly? and so on. Have a look at the Rails Guide on debugging
and it will show you techniques that you can use to debug your code.

Colin