Input String Was not in acorrect format(i think exception errorr)

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace Bill
{
    public partial class Daily : Form
    {
        Store objStore = new Store(); 
        public Daily()
        {
            InitializeComponent();
        }

        private void dateTimePicker1_ValueChanged(object sender, EventArgs e)
        {
            string date1 = dateTimePicker1.Text;            
            DateTime dat = DateTime.Parse(date1.ToString());
            string dat1 = dat.ToShortDateString();
            objStore.date = dat1.ToString();

            int S, X, Y;
            if (objStore.GetData())
            {
                S = objStore.price;
                lblSalesIncome.Text = S.ToString();
            }          
            else 
            {
               S=0;
            }

            if (objStore.GetSum())
            {
                X = objStore.price;
                lblPurchaseExpense.Text = X.ToString();
            }
            else
            {
                X = 0;
            }
            if (objStore.GetExpense())
            {
                Y = objStore.total;
                lblExpense.Text = Y.ToString();
            }
            else
            {
                Y = 0;
            }
            int totalIncomne = S;
            int expense = X + Y;
            lblExpTotal.Text = expense.ToString();
            lblTotalIncome.Text = S.ToString();
            int ss = totalIncomne - expense;
            lblbal.Text = ss.ToString();
        }

        private void Daily_Load(object sender, EventArgs e)
        {
            string date = dateTimePicker1.Text;
            int S, X, Y;
            DateTime dat =DateTime.Parse(date.ToString());
            string dat1 = dat.ToString("MM/dd/yyyy");
            objStore.date = dat1.ToString();
            if (objStore.GetData())
            {
                S = objStore.price;
                lblSalesIncome.Text = S.ToString();
            }

            else
            {
                S = 0;
            }

            if (objStore.GetSum())
            {
                X = objStore.price;
                lblPurchaseExpense.Text = X.ToString();
            }
            else
            {
                X = 0;
            }
            if (objStore.GetExpense())
            {
                Y = objStore.total;
                lblExpense.Text = Y.ToString();
            }
            else
            {
                Y = 0;
            }
            int totalIncomne = S;
            int expense = X + Y;
            lblExpTotal.Text = expense.ToString();
            lblTotalIncome.Text = S.ToString();
            int ss = totalIncomne - expense;
            lblbal.Text = ss.ToString();
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Billing.Dal;
using System.Data.SqlClient;
using System.Data;
namespace Bill
{
    class Store
    {
public string date { get; set; }

internal bool GetData()
        {
            DalLayer objdal = new DalLayer();
            SqlCommand cmd = new SqlCommand("select sum(Total) from tblSalesEntry where Date=@Date");
            cmd.Parameters.Add("@Date", SqlDbType.VarChar).Value = date;
            DataTable dt = objdal.CudReturnDataTable(cmd);
            if (dt.Rows.Count > 0)
            {
                price = Convert.ToInt32(dt.Rows[0][0].ToString());
                return true;
            }
            else
            {
                return false;
            }
        }

        internal bool GetSum()
        {
            DalLayer objdal = new DalLayer();
            SqlCommand cmd = new SqlCommand("select sum(Price) from tblPurchase where Date=@Date");
            cmd.Parameters.Add("@Date", SqlDbType.VarChar).Value = date;
            DataTable dt = objdal.CudReturnDataTable(cmd);
            if (dt.Rows.Count > 0)
            {
                price = Convert.ToInt32(dt.Rows[0][0].ToString());
                return true;
            }
            else
            {
                return false;
            }
        }

        internal bool GetExpense()
        {
            DalLayer objdal = new DalLayer();
            SqlCommand cmd = new SqlCommand("select sum(fldAdvance) from tblExp where Date=@Date");
            cmd.Parameters.Add("@Date", SqlDbType.VarChar).Value = date;
            DataTable dt = objdal.CudReturnDataTable(cmd);
            if (dt.Rows.Count > 0)
            {
                total = Convert.ToInt32(dt.Rows[0][0].ToString());
                return true;
            }
            else
            {
                return false;
            }
        }
}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

/// <summary>
/// Summary description for Dal
/// </summary>
/// 
namespace Billing.Dal
{
    public class DalLayer
    {
        #region Variables
        public string conStr = ConfigurationManager.ConnectionStrings["Bill.Properties.Settings.BillConnectionString"].ConnectionString;

        public DalLayer()
        { }
        #endregion
public DataTable CudReturnDataTable(SqlCommand cmd)
        {
            SqlConnection con = new SqlConnection();
            SqlDataAdapter da = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            con.ConnectionString = conStr;
            try
            {
                using (con)
                {
                     cmd.Connection = con;
                    con.Open();
                    SqlTransaction trans = con.BeginTransaction();
                    using (cmd)
                    {
                        using (trans)
                        {
                            try
                            {
                                cmd.Transaction = trans;
                                da.Fill(dt);
                                da.Dispose();
                                cmd.Parameters.Clear();
                                trans.Commit();
                            }
                            catch (Exception ex)
                            {
                                trans.Rollback();
                            }
                        }
                    }

                }
            }
            catch (Exception ex)
            {
                System.Diagnostics.Trace.WriteLine("[ValidateUser] Exception " + ex.Message);
            }

            return dt;
        }