Getting error after delete a row in datatable

Question

I have a form with 2 listbox and 2 datagridview which binding with 2 different datatable. Once I move a row to another datatable by clicking btn_go, I will get the error if I select another item in lbox_tableA

An unhandled exception of type 'System.Data.DeletedRowInaccessibleException' occurred in System.Data.dll

Additional information: Deleted row information cannot be accessed through the row.

Here is my code:

Dim bsourceA As New BindingSource
Dim bsourceB As New BindingSource
Dim dt_tableA As DataTable
Dim dt_tableB As DataTable
Dim drowA As DataRow
Dim drowB As DataRow

     Private Sub RefreshItemList(dt As DataTable)
        lbox_tableA.Items.Clear()

        dt_tableA = dt.Copy
        dt_tableB = dt.Clone

        dt_tableA.AcceptChanges()
        dt_tableB.AcceptChanges()

        bsourceA.DataSource = dt_tableA
        DataGridView1.DataSource = bsourceA
        DataGridView1.Refresh()
        lbox_tableA.DataSource = bsourceA
        lbox_tableA.DisplayMember = "item_name"

        bsourceB.DataSource = dt_tableB
        DataGridView2.DataSource = bsourceB
        DataGridView2.Refresh()
        lbox_tableB.DataSource = bsourceB
        lbox_tableB.DisplayMember = "item_name"
    End Sub

    Private Sub lbox_tableA_SelectedIndexChanged(sender As Object, e As EventArgs) Handles lbox_tableA.SelectedIndexChanged
        Dim currLbox As ListBox = sender
        Dim index As Integer = currLbox.SelectedIndex
        If index > -1 Then
            Dim drow As DataRow = dt_tableA.Rows(index)
            tb_qty.Text = drow.Item("item_qty").ToString      'ERROR 1 ON THIS LINE
            drowA = drow
        End If
    End Sub

    Private Sub lbox_tableB_SelectedIndexChanged(sender As Object, e As EventArgs) Handles lbox_tableB.SelectedIndexChanged
        Dim currLbox As ListBox = sender
        Dim index As Integer = currLbox.SelectedIndex
        If index > -1 Then
            Dim drow As DataRow = dt_tableB.Rows(index)
            tb_qty.Text = drow.Item("item_qty").ToString
            drowB = drow
        End If
    End Sub

    Private Sub btn_go_Click(sender As Object, e As EventArgs) Handles btn_go.Click
        If btn_go.Text = ">>>" Then
            If drowA.Item("item_qty") = tb_qty.Text Then
                dt_tableB.ImportRow(drowA)
                drowA.Delete()
            End If
        ElseIf btn_go.Text = "<<<" Then
            If drowB.Item("item_qty") = tb_qty.Text Then        'ERROR 2 ON THIS LINE
                dt_tableA.ImportRow(drowB)
                drowB.Delete()
            End If
        End If
    End Sub

Another problem is I can only move item in A to B, if I move item in B to A I get this error

An unhandled exception of type 'System.NullReferenceException' occurred in XXX.exe

Additional information: Object reference not set to an instance of an object.

How can I solve the issue?