How to resolve 'string was not recoganized as a valid datetime'

if (date != "" && date != null)
           {
               System.Globalization.DateTimeFormatInfo info = new System.Globalization.DateTimeFormatInfo();
               info.ShortDatePattern = "MM/dd/yyyy"
               DateTime ddate = DateTime.ParseExact(date, "dd/MM/yyyy", null);//here the error occures "string was not recoganized as a valid datetime"
               Userdir = (from u in Userdir where u.RegisteredDate >= ddate select u).OrderByDescending(c => c.RegisteredDate).ToList();
           }