string was not recognizes for valid date time...

ALTER procedure [dbo].[selectdate]

@CrtDate nvarchar(50)

begin

select top 1 Dates from General_Cash_Flow where CrtDate=@CrtDate order by CONVERT(nvarchar(50),Dates,120) Desc

end

my code

cmd = new SqlCommand("selectdate", cnn);

cmd.CommandType = CommandType.StoredProcedure;

cmd.Parameters.Add("CrtDate", SqlDbType.VarChar).Value = login.setvalueyear;

dr = cmd.ExecuteReader();

if (dr.Read())

{

string ddt = dr["Dates"].ToString();

dtpckVoucherDate.Text = string.Format("{0:dd/MM/yyyy}", ddt);

}

dr.Close();

i have different-different date max date show in ddt but in datetimepicker not show max date

and give error string was not recognized for valid date time ....