unity 5.3.1下使用oss报错

hi，我在unity5.3.1下使用阿里云的netsdk，访问oss，报错，如下：

NullReferenceException: Object reference not set to an instance of an object
Aliyun.OSS.Common.Communication.HttpExtensions.AddInternal (System.Net.WebHeaderCollection headers, System.String key, System.String value)
Aliyun.OSS.Common.Communication.HttpFactory.SetRequestHeaders (System.Net.HttpWebRequest webRequest, Aliyun.OSS.Common.Communication.ServiceRequest serviceRequest, Aliyun.OSS.Common.ClientConfiguration configuration)
Aliyun.OSS.Common.Communication.HttpFactory.CreateWebRequest (Aliyun.OSS.Common.Communication.ServiceRequest serviceRequest, Aliyun.OSS.Common.ClientConfiguration configuration)
Aliyun.OSS.Common.Communication.ServiceClientImpl.SendCore (Aliyun.OSS.Common.Communication.ServiceRequest serviceRequest, Aliyun.OSS.Common.Communication.ExecutionContext context)
Aliyun.OSS.Common.Communication.ServiceClient.Send (Aliyun.OSS.Common.Communication.ServiceRequest request, Aliyun.OSS.Common.Communication.ExecutionContext context)
Aliyun.OSS.Common.Communication.RetryableServiceClient.SendImpl (Aliyun.OSS.Common.Communication.ServiceRequest request, Aliyun.OSS.Common.Communication.ExecutionContext context, Int32 retryTimes)

测试，在net2013下的控制台是可以访问的，难道在unity下需要设置什么吗？