If you are using a datetime datatype in SQL, it has no notion of format. It just stores the datetime information as a numeric value, the format only becomes relevant when presenting the data to the end user; thus, in the ASP.NET side.
If you are storing the datetime values as string, then you are not using the proper datatype and you will run into several difficulties sooner or later. You should change that as soon as possible, or be prepared to poor performances of your queries on filtering/grouping by date fields. If you still don't want to use the proper datatype, then you will have to match the format in the database with the format of the
method. In this case, try
DateTime fromDate = DateTime.ParseExact(date, "yyyy/MM/dd", CultureInfo.InvariantCulture);