Когда я попытаюсь отредактировать данные, он выдаст ошибку "входная строка была не в правильном формате". в строке "totalpc=totalpc+convert.toint32(row.cells[2].text)"

private void calculateSum()
{
    Int32 TotalPC = 0;
    foreach (GridViewRow row in GridView1.Rows)
    {
        TotalPC = TotalPC + Convert.ToInt32(row.Cells[2].Text);
    }
    GridView1.FooterRow.Cells[1].Text = "Total PC";
    GridView1.FooterRow.Cells[2].Text = TotalPC.ToString();

}

protected void GridView1_DataBound(object sender, EventArgs e)
{
    calculateSum();
}

<form id="form1" runat="server">
        <h2><a href="/KB/answers/Mainpage.aspx" style="color:darkorange;text-decoration:none">Total User PCs in Active</a></h2>
        <div>

            <asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" DeleteCommand="DELETE FROM [TotalAll] WHERE [No] = @No" InsertCommand="INSERT INTO [TotalAll] ([No], [Department], [TotalPC]) VALUES (@No, @Department, @TotalPC)" SelectCommand="SELECT * FROM [TotalAll]" UpdateCommand="UPDATE [TotalAll] SET [Department] = @Department, [TotalPC] = @TotalPC WHERE [No] = @No">
                <DeleteParameters>
                    <asp:Parameter Name="No" Type="Int32" />
                </DeleteParameters>
                <InsertParameters>
                    <asp:Parameter Name="No" Type="Int32" />
                    <asp:Parameter Name="Department" Type="String" />
                    <asp:Parameter Name="TotalPC" Type="Int32" />
                </InsertParameters>
                <UpdateParameters>
                    <asp:Parameter Name="Department" Type="String" />
                    <asp:Parameter Name="TotalPC" Type="Int32" />
                    <asp:Parameter Name="No" Type="Int32" />
                </UpdateParameters>
            </asp:SqlDataSource>
            <br />
            <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" BackColor="White" BorderColor="#CC9966" BorderStyle="None" BorderWidth="1px" CellPadding="4" DataKeyNames="No" DataSourceID="SqlDataSource1" OnDataBound="GridView1_DataBound" ShowFooter="True" >
                <Columns>
                    <asp:BoundField DataField="No" HeaderText="No" ReadOnly="True" SortExpression="No" />
                    <asp:BoundField DataField="Department" HeaderText="Department" SortExpression="Department" />
                    <asp:BoundField DataField="TotalPC" HeaderText="TotalPC" SortExpression="TotalPC" />
                    <asp:CommandField HeaderText="Operation" ShowEditButton="True" />
                </Columns>
                <FooterStyle BackColor="#FFFFCC" ForeColor="#330099" />
                <HeaderStyle BackColor="#990000" Font-Bold="True" ForeColor="#FFFFCC" />
                <PagerStyle BackColor="#FFFFCC" ForeColor="#330099" HorizontalAlign="Center" />
                <RowStyle BackColor="White" ForeColor="#330099" />
                <SelectedRowStyle BackColor="#FFCC66" Font-Bold="True" ForeColor="#663399" />
                <SortedAscendingCellStyle BackColor="#FEFCEB" />
                <SortedAscendingHeaderStyle BackColor="#AF0101" />
                <SortedDescendingCellStyle BackColor="#F6F0C0" />
                <SortedDescendingHeaderStyle BackColor="#7E0000" />
            </asp:GridView>

        </div>
    </form>