ruby on rails - nested form triggering a 'Can't mass-assign protected attributes warning -

i've got multi layer nested form

 user->tasks->prerequisites  

and in same form

 user->tasks->location 

the location form works fine, i'm trying specify prerequisites current task. prerequisite task_id stored in :completed_task field.

when submit form, following error in output

 warning: can't mass-assign protected attributes: prerequisite_attributes 

one warning each task in user.

i've gone through other questions related this, ensuring field name :completed_task being referenced correctly,

adding attr_accessible model (it there , extended it).

i'm not sure else i'm supposed doing.

my models like

 class task < activerecord::base      attr_accessible :user_id, :date, :description, :location_id       belongs_to :user      has_one :location      accepts_nested_attributes_for :location       has_many :prerequisites      accepts_nested_attributes_for :prerequisites end  class prerequisite < activerecord::base      attr_accessible :completed_task       belongs_to :task end 

the form uses formtastic, , i'm including form via

 <%= f.semantic_fields_for :prerequisites |builder3| %>     <%= render 'prerequisite_fields', :f=>builder3 %> <% end %>  --- _prerequisite_fields.html.erb ----- < div class="nested-fields" >    <%= f. inputs:completed_step %> </div> 

any suggestions?

add :prerequisite_attributes attr_accessible in order mass-assign

attr_accessible :user_id, :date, :description, :location_id, :prerequisite_attributes

should started.