Error on update for a 3 columns join table

I have a problem while updating a 3 keys join table. I've been on this for quite a while now and have no idea how to fix it. In short, to be able to get the new project working, I had to set these two habtm declaration (in /models/project.rb):

    has_and_belongs_to_many :users,         :join_table => "projects_roles_users",         :foreign_key => 'property_id',         :association_foreign_key => 'user_id',         :insert_sql => 'INSERT INTO                     projects_roles_users(project_id,role_id,user_id)                     VALUES(#{id}, #{role_ids}, #{user_ids})',         :delete_sql => 'DELETE FROM projects_roles_users                         WHERE projects_roles_users.property_id = #{id}'

      has_and_belongs_to_many :roles,          :join_table => "projects_roles_users",          :foreign_key => 'project_id',          :association_foreign_key => 'role_id',          :insert_sql => 'INSERT INTO                     projects_roles_users(project_id,role_id,user_id)                     VALUES(#{id}, #{role_ids}, #{user_ids})',          :delete_sql => 'DELETE FROM projects_roles_users                          WHERE projects_roles_users.project_id = #{id}'

So the new project works just fine (although I get duplicates in project_roles_users). However, when I want to update the role a user has in a project, I get this error:

    Mysql::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' 1414)' at line 3: INSERT INTO                     projects_roles_users(project_id,role_id,user_id)                     VALUES(29, , )

Here's the controller:

      def update         @project = Project.find(params[:id])

        respond_to do |format|           if @project.update_attributes(params[:project])             flash[:notice] = 'Project was successfully updated.'             format.html { redirect_to user_path(current_user.id) }             format.xml { head :ok }           else             format.html { render :action => "edit" }             format.xml { render :xml => @project.errors, :status => :unprocessable_entity }           end         end       end

And here's the view:

  <% form_for(@project,:html => { :multipart => true }) do |f| %>     <%= f.error_messages %>

    <p>     <%= f.label :name %><br />     <%= f.text_field :name %>     </p>

    <p>     <% f.label :role, 'Role' %><br />     <%= f.collection_select :role_ids, Role.find(:all, :order => 'position'), :id, :role, {}, :multiple => false %>     </p>

    <%= f.hidden_field :user_ids, :value => current_user.id %>

    <p>     <%= f.submit 'Update' %>     </p>   <% end %>

  <%= link_to 'Show', @project %> |   <%= link_to 'Back', projects_path %>   <%= javascript_tag "$('address').focus()" %>

Finally, here's the log (maybe it'll help you figure it out...):

    Processing ProjectsController#update (for 127.0.0.1 at 2011-02-23 08:43:29) [PUT]       Parameters: {"project"=>{"price"=>"12$", "city"=>"City", "address"=>"452 Street st.", "user_ids"=>"14", "role_ids"=>["2"], "postalcode"=>"12346", "description"=>"Description", "state"=>"State"}, "commit"=>"Update", "authenticity_token"=>"OKQaW4LPb3Xye6Kbh/W2EgxPWFe4aj26etIEVlCTKTg=", "id"=>"29"}       User Columns (0.9ms) SHOW FIELDS FROM `users`       User Load (0.1ms) SELECT * FROM `users` WHERE (`users`.`id` = 14) LIMIT 1       Page Load (0.1ms) SELECT * FROM `pages` WHERE (parent_id IS NULL) ORDER BY position       Project Columns (0.9ms) SHOW FIELDS FROM `projects`       Project Load (0.1ms) SELECT * FROM `projects` WHERE (`properties`.`id` = 29)       SQL (0.1ms) BEGIN       Role Columns (0.8ms) SHOW FIELDS FROM `roles`       Role Load (0.1ms) SELECT * FROM `roles` WHERE (`roles`.`id` = 2)       projects_roles_users Columns (0.5ms) SHOW FIELDS FROM `projects_roles_users`       Role Load (0.3ms) SELECT * FROM `roles` INNER JOIN `projects_roles_users` ON `roles`.id = `projects_roles_users`.role_id WHERE (`projects_roles_users`.project_id = 29 )       User Load (0.3ms) SELECT `users`.id FROM `users` INNER JOIN `projects_roles_users` ON `users`.id = `projects_roles_users`.user_id WHERE (`projects_roles_users`.project_id = 29 )       SQL (0.1ms) DELETE FROM projects_roles_users      WHERE projects_roles_users.project_id = 29       User Load (0.2ms) SELECT `users`.id FROM `users` INNER JOIN `projects_roles_users` ON `users`.id = `properties_roles_users`.user_id WHERE (`projects_roles_users`.project_id = 29 )       SQL (0.1ms) DELETE FROM projects_roles_users      WHERE projects_roles_users.project_id = 29       SQL (0.5ms) describe `projects_roles_users`       User Load (0.3ms) SELECT `users`.id FROM `users` INNER JOIN `projects_roles_users` ON `users`.id = `projects_roles_users`.user_id WHERE (`projects_roles_users`.project_id = 29 )       SQL (0.0ms) Mysql::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' 1414)' at line 3: INSERT INTO      projects_roles_users(project_id,role_id,user_id)      VALUES(29, , )       SQL (0.1ms) ROLLBACK

    ActiveRecord::StatementInvalid (Mysql::Error: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ' 1414)' at line 3: INSERT INTO                     projects_roles_users(project_id,role_id,user_id)                     VALUES(29, , )):       app/controllers/properties_controller.rb:71:in `update'       app/controllers/properties_controller.rb:70:in `update'

    Rendered rescues/_trace (136.5ms)     Rendered rescues/_request_and_response (0.6ms)     Rendering rescues/layout (internal_server_error)