iframe无法在带有form_for的rails 4中工作？

Question

目前我正在将我的应用程序从rails 3升级到rails 4。 升级后iframe无法使用form_for抛出以下错误。

    ActionController::UnknownFormat (ActionController::UnknownFormat):

here is mycode:
<%= form_for note_collection,:url=> lease_suites_create_path(portid,propid), :html=>{:target => "lease_suites_frame", :multipart => true,:id=>"mgmt_suites_form"} do |p| -%>
---
----
---
    <a href="javascript:;" class="btn-grey newtask-btn" id ="suite_add_id"> <span class="addProspect">submit</span></a>
<%end%>

and  i am submitting my form with jquery ajax.
here is iframe:
<iframe id="lease_suites_frame" name="lease_suites_frame" style="display: none">