使用Get方法获取token报错

.net 使用HttpWebRequest获取gettoken时获取token时。不同的机器有些报错，有些正常，同一台机器有时报错，有时可以正常获取。错误信息如下

捕捉到 System.Net.WebException
  Message=基础连接已经关闭: 发送时发生错误。
  Source=System
  StackTrace:
       在 System.Net.HttpWebRequest.GetResponse()
       在 ConsoleApplication4.HttpHelper.InternalHttp(HttpMethod method, String url, Byte[] bytes, CookieContainer cookieContainer, Encoding encoding, Dictionary`2 others) 位置 c:\users\yjj\documents\visual studio 2010\Projects\ConsoleApplication4\ConsoleApplication4\httphelper.cs:行号 248
  InnerException: System.IO.IOException
       Message=从传输流收到意外的 EOF 或 0 个字节。
       Source=System
       StackTrace:
            在 System.Net.FixedSizeReader.ReadPacket(Byte[] buffer, Int32 offset, Int32 count)
            在 System.Net.Security.SslState.StartReadFrame(Byte[] buffer, Int32 readBytes, AsyncProtocolRequest asyncRequest)
            在 System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
            在 System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
            在 System.Net.Security.SslState.StartSendBlob(Byte[] incoming, Int32 count, AsyncProtocolRequest asyncRequest)
            在 System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
            在 System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
            在 System.Net.TlsStream.CallProcessAuthentication(Object state)
            在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
            在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
            在 System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
            在 System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
            在 System.Net.PooledStream.Write(Byte[] buffer, Int32 offset, Int32 size)
            在 System.Net.ConnectStream.WriteHeaders(Boolean async)
       InnerException: