Problem in row adding event in Editing Core RowAdding Event

 
protected void WebDataGrid1_RowAdding(object sender, Infragistics.Web.UI.GridControls.RowAddingEventArgs e)
{
SqlConnection con = new SqlConnection(connectionString);
SqlCommand cmd = new SqlCommand("InsertDailyElectricityDetails", con);
con.Open();
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("@machine", WebDataGrid1.Rows[0].Items[1].Value);
cmd.Parameters.AddWithValue("@lastdayreading", WebDataGrid1.Rows[0].Items[2].Value);
cmd.Parameters.AddWithValue("@currentdayreading", WebDataGrid1.Rows[0].Items[3].Value);
cmd.ExecuteNonQuery();
con.Close();
}

ALTER PROCEDURE dbo.InsertDailyElectricityDetails
	
	(
	@machine varchar,
	@lastdayreading DECIMAL,
	@currentdayreading DECIMAL 
	
	)
	
AS
INSERT INTO ElectricityDailyMeterReadings
            (MachineID,LastDayMeterReading,CurrentDayMeterReading,Consumption)
VALUES      (@machine,@lastdayreading,@currentdayreading,@currentdayreading - @lastdayreading)	
	RETURN