1090 error occurs in Flash Builder, but update action works fine in Rails

Question

The below student_request method updates records successfully in Rails but returns "Error #1090: XML parser failure: element is malformed.” in Flash Builder 4 beta. Now the xml works fine for other actions, so I don't think the xml is at fault. It's something in the confirm_request method. Does anyone have any idea?

class StudentRequestsController < RestfulController
def confirm_request
 StudentRequest.transaction do   
update_common do |student_request|    
student_request.creator_id = current_user.contact.contactable
student_request.student_request_status_id = 1
if student_request.save
x = student_request.destination_id
y = student_request.id
end
books = Book.find(:all, :conditions => ["books.location_id = ? && books.student_request_id = ?", x, y])
 books.each do |book|
 book.student_book = 3
 book.save
end
end
end
end

class RestfulController < ApplicationController

def update
update_common { |resource| update_resource(resource) }
end

 def update_common(verb="updated")
 @resource = find_one_resource params[:id]
 self.resource = @resource

 respond_to do |format|
   if yield(@resource)

     format.xml  {head :ok }

   else

     format.xml  { render :xml  => @resource.errors.to_xml (:skip_types => true, :dasherize => false),  :status => :unprocessable_entity }

   end
   end

def find_one_resource(id)
 resource_model.find(id)
 end

  def update_resource(resource)
 resource.update_attributes update_resource_params
  end

 def update_resource_params
 params[resource_params_key]
 end