403 Error on AJAX Request in add new item (collection field) I have normal content type which has 12 collection fields 
each field has unlimited value
when i try to click add new item on any field it gives me ajax error

An AJAX HTTP error occurred.
HTTP Result Code: 403
Debugging information follows.
Path: /?q=system/ajax
StatusText: Forbidden
ResponseText:


I have another content type and also has collection field with unlimited value .. but it works without any problem
so please help me why some content type has error and the other doesn't have

by the way: i use D7 and i upgraded it to 7.35 but this problem was before the upgrading

i have checked all the answers in the Drupal Answers but unfortunately did it help 

edit:

ResponseText:
@import url("http://example.org/modules/system/system.base.css?nlmla7");
@import url("http://example.org/modules/system/system.base-rtl.css?nlmla7");
@import url("http://example.org/modules/system/system.menus.css?nlmla7");
@import url("http://example.org/modules/system/system.menus-rtl.css?nlmla7");
@import url("http://example.org/modules/system/system.messages.css?nlmla7");
@import url("http://example.org/modules/system/system.messages-rtl.css?nlmla7");
@import url("http://example.org/modules/system/system.theme.css?nlmla7");
@import url("http://example.org/modules/system/system.theme-rtl.css?nlmla7");
@import url("http://example.org/sites/all/modules/date/date_api/date.css?nlmla7");
@import url("http://example.org/sites/all/modules/date/date_api/date-rtl.css?nlmla7");
@import url("http://example.org/sites/all/modules/date/date_popup/themes/datepicker.1.7.css?nlmla7");
@import url("http://example.org/sites/all/modules/date/date_repeat_field/date_repeat_field.css?nlmla7");
@import url("http://example.org/modules/field/theme/field.css?nlmla7");
@import url("http://example.org/modules/field/theme/field-rtl.css?nlmla7");
@import url("http://example.org/sites/all/modules/field_hidden/field_hidden.css?nlmla7");
@import url("http://example.org/modules/node/node.css?nlmla7");
@import url("http://example.org/sites/all/modules/recieve_orders/css/orders_styles.css?nlmla7");
@import url("http://example.org/modules/search/search.css?nlmla7");
@import url("http://example.org/modules/search/search-rtl.css?nlmla7");
@import url("http://example.org/modules/user/user.css?nlmla7");
@import url("http://example.org/modules/user/user-rtl.css?nlmla7");
@import url("http://example.org/sites/all/modules/views/css/views.css?nlmla7");
@import url("http://example.org/sites/all/modules/views/css/views-rtl.css?nlmla7");
@import url("http://example.org/sites/all/modules/admin_menu/admin_menu.css?nlmla7");
@import url("http://example.org/sites/all/modules/admin_menu/admin_menu-rtl.css?nlmla7");
@import url("http://example.org/sites/all/modules/admin_menu/admin_menu.uid1.css?nlmla7");
@import url("http://example.org/sites/all/modules/ctools/css/ctools.css?nlmla7");
@import url("http://example.org/sites/all/modules/adminimal_admin_menu/adminimal_admin_menu.css?nlmla7");
@import url("http://example.org/modules/shortcut/shortcut.css?nlmla7");
@import url("http://example.org/modules/shortcut/shortcut-rtl.css?nlmla7");
@import url("http://example.org/sites/all/themes/adminimal_theme/css/reset.css?nlmla7");
@import url("http://example.org/sites/all/themes/adminimal_theme/css/style.css?nlmla7");
@import url("http://example.org/sites/all/themes/adminimal_theme/css/style-rtl.css?nlmla7");
@import url("http://example.org/sites/all/themes/adminimal_theme/css/mobile.css?nlmla7");
@import url("http://example.org/sites/all/themes/adminimal_theme/css/tablet.css?nlmla7");ySite.org/sites/all/themes/adminimal_theme/css/tablet.css?nlmla7"); 


and there are too many custom modules in my site

but the thing which make me more conflicted is why it doesn't give error in the other content type
for what it's worth we just wrestled with this for a while on our own sites. The solution actually ended up being disabling cloudflare on 'system/ajax' URLs. If you're running CF and have this problem - try it!