[]post提交问题

XMLHttpRequest cannot load http://xxx.xxx.xxx/subData. No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'file://' is therefore not allowed access. The response had HTTP status code 500.
后台是用c#写的，请问出现这问题怎么解决，提交图片是OK的，提交数据出现上述情况