<span id="add_link"><%= link_to_function "Add a Review", "Element.show('add_review');Element.hide('add_link');" %></span>
<div id="add_review" style="display:none">
<br><h3>Add a review</h3>
<% form_remote_tag(:update => 'add_review',
                   :url => {:controller => 'review', :action => 'create', :id => @item}, :method=>:put) do |f| %>
  <%= f.text_area :review_text, :rows => 3 %><br>
  <%= submit_tag 'Add review!'%>
<% end %>
</div>





You have a nil object when you didn't expect it!
The error occurred while evaluating nil.text_area