Collection was modified; enumeration operation may not execute.

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VB

Below Is My Code for Window Application :

Imports System.Data
Imports System.Data.SqlClient
Imports System.Configuration
Public Class frmTrialBalanceNew
    Dim objdb As New DataSave
    Protected Overrides ReadOnly Property CreateParams() As CreateParams
        Get
            Dim param As CreateParams = MyBase.CreateParams
            param.ClassStyle = param.ClassStyle Or &H200
            Return param
        End Get
    End Property
    Private Sub frmTrialBalanceNew_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Try
            'Form is in center ---------------------------------------------
            MaximizeBox = False
            Dim boundWidth As Integer = Screen.PrimaryScreen.Bounds.Width
            Dim boundHeight As Integer = Screen.PrimaryScreen.Bounds.Height
            Dim x As Integer = boundWidth - Me.Width
            Dim y As Integer = boundHeight - Me.Height
            Me.Location = New Point(x / 2, y / 2)

            '---------------------------------------------------------------

            Dim purchase, exp As Double

            Dim datefrom As Date = frmTrialBalanceDate.DateFrom.Text
            lblDatefrom.Text = frmTrialBalanceDate.DateFrom.Text
            Dim Dateto As Date = frmTrialBalanceDate.DateTo.Text
            lblDateTo.Text = frmTrialBalanceDate.DateTo.Text
            purchase = Val(objdb.GetValue("select SUM(Amount) from tbl_StockTransaction where EntryType = 'Stock Purchase' and companyid = '" & strcompanyid & "' and EntryDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103)"))
            exp = Val(objdb.GetValue("select SUM(Freight) + SUM(Labour) from PurchaseNew where PurchaseBillNo is not NULL and companyid = '" & strcompanyid & "' and PurchaseBillDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103)"))
            lblPurchase.Text = Val(purchase) + Val(exp)
            'lblPurchase.Text = Val(objdb.GetValue("select SUM(Amount) from tbl_StockTransaction where EntryType = 'Stock Purchase' and companyid = '" & strcompanyid & "'"))

            lblOpeningStock.Text = Val(objdb.GetValue("select SUM(Amount) from tbl_StockTransaction where EntryType = 'Opening Stock' and companyid = '" & strcompanyid & "' and EntryDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103)"))
            lblPurchaseReturn.Text = Val(objdb.GetValue("select SUM(Amount) from tbl_StockTransaction where EntryType = 'Purchase Return' and companyid = '" & strcompanyid & "' and EntryDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103)"))
            lblTotalPurchase.Text = (Val(lblPurchase.Text) + Val(lblOpeningStock.Text)) - Val(lblPurchaseReturn.Text)
            lblCrgInwards.Text = Val(objdb.GetValue("select SUM(Labour) from SalesNew where InvoiceNO is Not NULL and companyid = '" & strcompanyid & "' and InvoiceDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103)"))
            lblWages.Text = Val(objdb.GetValue("select SUM(Freight) from SalesNew where InvoiceNo is Not NULL and companyid = '" & strcompanyid & "' and InvoiceDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103)"))

            'lblClosingStockAmount.Text = Val(objdb.GetValue("select SUM(Amount) from tbl_StockTransaction where companyid = '" & strcompanyid & "' and EntryDate Between '" & datefrom & "' and '" & Dateto & "'"))

            Dim ds As New DataSet
            Dim closingstock As Double = "0"
            ds = objdb.ReturnDS("select (SUM(B.Qty) * A.CostPrice) as [TotalAmount] from tbl_StockTransaction B,tbl_ItemMaster A where B.EntryDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103) and A.ItemCode = B.ProductCode and B.companyid = '" & strcompanyid & "' group by A.CostPrice")
            For count = 0 To ds.Tables(0).Rows.Count - 1
                Dim totalamount As Double = ds.Tables(0).Rows(count)("TotalAmount")
                closingstock = closingstock + totalamount
            Next
            lblClosingStockAmount.Text = closingstock


            lblsales.Text = Val(objdb.GetValue("select SUM(AMount) from tbl_StockTransaction where EntryType = 'Stock Sell' and companyid = '" & strcompanyid & "' and EntryDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103)"))
            lblsalesreturn.Text = Val(objdb.GetValue("select SUM(AMount) from tbl_StockTransaction where companyid = '" & strcompanyid & "'and EntryType = 'Sales Return' and EntryDate Between convert(datetime,'" & datefrom & "',103) and convert(datetime,'" & Dateto & "',103)"))
            lblTotalSales.Text = Val(lblsales.Text) + Val(lblsalesreturn.Text)


            Dim debitsidetotal, creditsidetotal As Double
            debitsidetotal = Val(lblTotalPurchase.Text) + Val(lblCrgInwards.Text) + Val(lblWages.Text)
            creditsidetotal = Val(lblClosingStockAmount.Text) + Val(lblTotalSales.Text)

            If debitsidetotal <= creditsidetotal Then
                lblTradingProfit.Text = Val(creditsidetotal) - Val(debitsidetotal)
                lblDrSideTotal.Text = Val(lblTradingProfit.Text) + Val(debitsidetotal)
                lblCrSideTotal.Text = creditsidetotal
                lblCRLoss.Visible = False
                lblCRPL.Visible = False
                lblDRPL.Visible = True
                lblDRProfit.Visible = True
                StrTrialBalance = lblTradingProfit.Text
            Else
                lblTradingLoss.Text = Val(debitsidetotal) - Val(creditsidetotal)
                lblDrSideTotal.Text = debitsidetotal
                lblCrSideTotal.Text = Val(lblTradingLoss.Text) + Val(creditsidetotal)
                lblCRLoss.Visible = True
                lblCRPL.Visible = True
                lblDRPL.Visible = False
                lblDRProfit.Visible = False
                StrTrialBalance = -lblTradingLoss.Text
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub

    Private Sub btnClose_Click(sender As Object, e As EventArgs) Handles btnClose.Click
        Try
            Me.Close()
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try

    End Sub
End Class

form Work Completely, When I Pres Close Button Give This Error.

Collection was modified; enumeration operation may not execute.

What I have tried:

Collection was modified; enumeration operation may not execute.
I am not using eny enumeration operation.
i am only use for loop and query