在Asp.net中提交上传图片出现403 authorization has expired

ajax请求error出现{"code":403,"url":"\/AssetImage\/26内装修.jpg","time":1445943563,"message":"authorization has expired","no-sign":"ce6b19e2398b0bbce117b1a242fb6eac"}
但是直接用表单提交成功的，用ajax就出现这个错误，请问这个是什么情况