IOException
   在 System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)
   在 System.IO.FileStream.WriteCore(Byte[] buffer, Int32 offset, Int32 count)
   在 System.IO.FileStream.FlushWrite(Boolean calledFromFinalizer)
   在 System.IO.FileStream.Flush(Boolean flushToDisk)
   在 System.Windows.Media.Imaging.BitmapDownload.ReadCallback(IAsyncResult result)
   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.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   在 System.Threading.ThreadPoolWorkQueue.Dispatch()