ASP.Net GridView Error: Unable to cast object of type CheckBox to type TextBox

I have verified the Table with the shared sample data.

You need to update the condition where you have to check if the value is empty then, don't set the column in the update statement.

Protected Sub GV1_RowUpdating(sender As Object, e As GridViewUpdateEventArgs) Handles GV1.RowUpdating
    Dim row As GridViewRow = GV1.Rows(e.RowIndex)
    Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(constr)
        Dim sql As String = "UPDATE " + lstTables.SelectedValue + " SET "
        For i = 2 To row.Cells.Count - 1
            Dim columnName As String = CType(GV1.HeaderRow.Cells(i).Controls(0), LinkButton).Text
            Dim columnValue As String = String.Empty
            Dim control As Control = row.Cells(i).Controls(0)
            Select Case control.GetType().Name
                Case "HyperLink"
                    columnValue = TryCast(control, HyperLink).Text
                    Exit Select
                Case "TextBox"
                    columnValue = TryCast(control, TextBox).Text
                    Exit Select
                Case "LinkButton"
                    columnValue = TryCast(control, LinkButton).Text
                    Exit Select
                Case "CheckBox"
                    columnValue = TryCast(control, CheckBox).Checked
                    Exit Select
            End Select
            ' Condition is checked if value is empty then skip it.
            If Not String.IsNullOrEmpty(columnValue) Then
                sql += String.Format("{0} = '{1}', ", columnName, columnValue)
            End If
        Next
        sql = sql.Substring(0, sql.LastIndexOf(", "))
        sql += String.Format(" WHERE {0} = '{1}'", CType(GV1.HeaderRow.Cells(1).Controls(0), LinkButton).Text, CType(row.Cells(1).Controls(0), TextBox).Text)
        Using cmd As SqlCommand = New SqlCommand(sql, con)
            con.Open()
            cmd.ExecuteNonQuery()
            con.Close()
        End Using
    End Using

    GV1.EditIndex = -1
    Me.GetData()
End Sub