Is the error on the "ListPeriods =" line? Is ListPeriods of type List<DataInfo>?
If so, if you look at the .Select you are selecting a string (w.AcceptanceDateOrder.ToString()) so when you ToList you get a List<string> which can't be assigned to List<DataInfo>. So your Select needs to return DataInfo so that ToList returns List<DataInfo>
viewModel.ListPeriods = listOrdersUsers.OrderBy (p => p.AcceptanceDateOrder
). Select (w => new DataInfo{Data = w.AcceptanceDateOrder.ToString().Substring(0, 7)}) ToList();