WebException
   在 System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult, TransportContext& context)
   在 System.Net.HttpWebRequest.EndGetRequestStream(IAsyncResult asyncResult)
   在 DynamicClass.WebDAVClient.ReadCallback(IAsyncResult result)
   在 System.Net.LazyAsyncResult.Complete(IntPtr userToken)
   在 System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   在 System.Net.ContextAwareResult.Complete(IntPtr userToken)
   在 System.Net.LazyAsyncResult.ProtectedInvokeCallback(Object result, IntPtr userToken)
   在 System.Net.HttpWebRequest.SetResponse(Exception E)
   在 System.Net.ConnectionReturnResult.SetResponses(ConnectionReturnResult returnResult)
   在 System.Net.Connection.CompleteConnectionWrapper(Object request, Object state)
   在 System.Net.PooledStream.ConnectionCallback(Object owningObject, Exception e, Socket socket, IPAddress address)
   在 System.Net.ServicePoint.ConnectSocketCallback(IAsyncResult asyncResult)
   在 System.Net.LazyAsyncResult.Complete(IntPtr userToken)
   在 System.Net.ContextAwareResult.Complete(IntPtr userToken)
   在 System.Net.LazyAsyncResult.ProtectedInvokeCallback(Object result, IntPtr userToken)
   在 System.Net.Sockets.Socket.ConnectCallback()
   在 System.Threading._ThreadPoolWaitOrTimerCallback.PerformWaitOrTimerCallback(Object state, Boolean timedOut)

SocketException
由于连接方在一段时间后没有正确答复或连接的主机没有反应，连接尝试失败。 60.190.91.196:11121
   在 System.Net.Sockets.Socket.InternalEndConnect(IAsyncResult asyncResult)
   在 System.Net.Sockets.Socket.EndConnect(IAsyncResult asyncResult)
   在 System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Socket s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state, IAsyncResult asyncResult, Exception& exception)