How to add new row in gridview in asp.net(C#) when we allow paging true and page size="5"

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ASP.NET

private void AddNewRow()
    {
        int rowIndex = 0;
        GridViewRow gvrow = grvStudentDetails.BottomPagerRow;
        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++)
                {
                    TextBox TextAmount = (TextBox)grvStudentDetails.Rows[rowIndex].Cells[1].FindControl("txtamount");
                    DropDownList dblmode = (DropDownList)grvStudentDetails.Rows[rowIndex].Cells[5].FindControl("dblmode");
                    TextBox TextBank = (TextBox)grvStudentDetails.Rows[rowIndex].Cells[2].FindControl("txtbank");
                    TextBox TextBranch = (TextBox)grvStudentDetails.Rows[rowIndex].Cells[3].FindControl("txtbranch");
                    TextBox TextCheque = (TextBox)grvStudentDetails.Rows[rowIndex].Cells[3].FindControl("txtcheque");
                    RadioButtonList RBLStatus = (RadioButtonList)grvStudentDetails.Rows[rowIndex].Cells[4].FindControl("rblstatus");
           



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


                    dtCurrentTable.Rows[i - 1]["Col1"] = TextAmount.Text;
                    dtCurrentTable.Rows[i - 1]["Col2"] = dblmode.SelectedValue;
                    dtCurrentTable.Rows[i - 1]["Col3"] = TextBank.Text;
                    dtCurrentTable.Rows[i - 1]["Col4"] = TextBranch.Text;
                    dtCurrentTable.Rows[i - 1]["Col5"] = TextCheque.Text;
                    dtCurrentTable.Rows[i - 1]["Col6"] = RBLStatus.SelectedValue;
                   


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

                grvStudentDetails.DataSource = dtCurrentTable;
                grvStudentDetails.DataBind();               


                TextBox txn = (TextBox)grvStudentDetails.Rows[rowIndex].Cells[1].FindControl("txtamount");
                txn.Focus();
              
            }
        }

I get "error=Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index".

PLZ help me