System.Net.Http.HttpRequestException: Error while copying content to a stream. ---> System.IO.IOException: Unable to read data from the transport connection: The connection was closed.
   at System.Net.ConnectStream.IOError(Exception exception, Boolean willThrow)
   at System.Net.ConnectStream.EndWrite(IAsyncResult asyncResult)
   at System.Threading.Tasks.TaskFactory`1.FromAsyncCoreLogic(IAsyncResult iar, Func`2 endFunction, Action`1 endAction, Task`1 promise, Boolean requiresSynchronization)
   --- End of inner exception stack trace ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at Insurance.Controller.ProposalController.<UploadfileondropboxnewAsync>d__6.MoveNext() in C:\CODES\MailProject\Insurance\Controller\ProposalController.cs:line 203