[c#] "Specified argument was out of the range of valid values"

I'm adding dynamic Rows in ASP.Net GridView Control with TextBoxes. But I'm getting the error below when I click on my Add New Row button.

Specified argument was out of the range of valid values. Parameter name: index

What could be the error ?

Th code in my .aspx file

<div id="Div1" class="divTable">
    <asp:gridview id="Gridview1" runat="server" autogeneratecolumns="false" gridlines="None"
        width="100%" height="100%">
            <Columns>
                <asp:TemplateField>
                    <ItemTemplate>
                        <div class="divRow">
                            <div class="divColumn">
                                <div>
                                    <asp:Label ID="lbl1" runat="server" Text="Type Name" CssClass="formLable"></asp:Label>
                                </div>
                                <div>
                                    <asp:TextBox ID="txt_type" Width="200" runat="server" CssClass="txtbox"></asp:TextBox>
                                </div>
                                <span>
                                    <asp:RequiredFieldValidator ID="TYPE_NAME_VAL" runat="server" ControlToValidate="txt_type"
                                        ErrorMessage="Type is required." Display="Dynamic" CssClass="error"></asp:RequiredFieldValidator>
                                </span>
                            </div>
                            <div class="divColumn">
                                <div>
                                    <asp:Label ID="lbl2" runat="server" Text="Total" CssClass="formLable"></asp:Label>
                                </div>
                                <div>
                                    <asp:TextBox ID="txt_total" Width="200" runat="server" CssClass="txtbox"></asp:TextBox>
                                </div>
                            </div>
                        </div>
                        <div class="divRow">
                            <div class="divColumn">
                                <div>
                                    <asp:Label ID="lbl3" runat="server" Text="Max" CssClass="formLable"></asp:Label>
                                </div>
                                <div>
                                    <asp:TextBox ID="txt_max" Width="200" runat="server" CssClass="txtbox"></asp:TextBox>
                                </div>
                            </div>
                            <div class="divColumn">
                                <div>
                                    <asp:Label ID="lbl4" runat="server" Text="Min" CssClass="formLable"></asp:Label>
                                </div>
                                <div>
                                    <asp:TextBox ID="txt_min" Width="200" runat="server" CssClass="txtbox"></asp:TextBox>
                                </div>
                            </div>
                            <div class="divColumn">
                                <div>
                                    <asp:Label ID="lbl5" runat="server" Text="Rate" CssClass="formLable"></asp:Label>
                                </div>
                                <div>
                                    <asp:TextBox ID="txt_rate" Width="200" runat="server" CssClass="txtbox"></asp:TextBox>
                                </div>
                            </div>
                        </div>
                        <asp:Button ID="ButtonAdd" runat="server" Text="Add New Row" OnClick="ButtonAdd_Click"
                            CausesValidation="False" />
                    </ItemTemplate>
                </asp:TemplateField>
            </Columns>
        </asp:gridview>
</div>

C# code of ButtonAdd_Click()

if (ViewState["CurrentTable"] != null)
{
    DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
    DataRow drCurrentRow = null;
    if (dtCurrentTable.Rows.Count > 0)
    {
        for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
        {
            //extract the TextBox values
            TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("txt_type");
            TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("txt_total");
            TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("txt_max");
            TextBox box4 = (TextBox)Gridview1.Rows[rowIndex].Cells[4].FindControl("txt_min");
            TextBox box5 = (TextBox)Gridview1.Rows[rowIndex].Cells[5].FindControl("txt_rate");

            drCurrentRow = dtCurrentTable.NewRow();

            dtCurrentTable.Rows[i - 1]["Column1"] = box1.Text;
            dtCurrentTable.Rows[i - 1]["Column2"] = box2.Text;
            dtCurrentTable.Rows[i - 1]["Column3"] = box3.Text;
            dtCurrentTable.Rows[i - 1]["Column4"] = box4.Text;
            dtCurrentTable.Rows[i - 1]["Column5"] = box5.Text;

            rowIndex++;
        }
        dtCurrentTable.Rows.Add(drCurrentRow);
        ViewState["CurrentTable"] = dtCurrentTable;

        Gridview1.DataSource = dtCurrentTable;
        Gridview1.DataBind();
    }
}
else
{
    Response.Write("ViewState is null");
}

try this.

if (ViewState["CurrentTable"] != null)
            {
                DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
                DataRow drCurrentRow = null;
                if (dtCurrentTable.Rows.Count > 0)
                {
                    for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
                    {
                        //extract the TextBox values
                        TextBox box1 = (TextBox)Gridview1.Rows[i].Cells[1].FindControl("txt_type");
                        TextBox box2 = (TextBox)Gridview1.Rows[i].Cells[2].FindControl("txt_total");
                        TextBox box3 = (TextBox)Gridview1.Rows[i].Cells[3].FindControl("txt_max");
                        TextBox box4 = (TextBox)Gridview1.Rows[i].Cells[4].FindControl("txt_min");
                        TextBox box5 = (TextBox)Gridview1.Rows[i].Cells[5].FindControl("txt_rate");

                        drCurrentRow = dtCurrentTable.NewRow();
                        drCurrentRow["RowNumber"] = i + 1;

                        dtCurrentTable.Rows[i - 1]["Column1"] = box1.Text;
                        dtCurrentTable.Rows[i - 1]["Column2"] = box2.Text;
                        dtCurrentTable.Rows[i - 1]["Column3"] = box3.Text;
                        dtCurrentTable.Rows[i - 1]["Column4"] = box4.Text;
                        dtCurrentTable.Rows[i - 1]["Column5"] = box5.Text;

                        rowIndex++;
                    }
                    dtCurrentTable.Rows.Add(drCurrentRow);
                    ViewState["CurrentTable"] = dtCurrentTable;

                    Gridview1.DataSource = dtCurrentTable;
                    Gridview1.DataBind();
                }
            }
            else
            {
                Response.Write("ViewState is null");
            }

I was also getting same issue as i tried using value 0 in non-based indexing,i.e starting with 1, not with zero