ASP.Net GridView cell value Error: Input string was not in a correct format

Hello,

I tried to update a checkbox in database but I hot this exception: 'Input string was not in a correct format.'

I share the code with you. I want to update a checkbox in database if it is checked.

    protected void chkRowPlatita_CheckedChanged(object sender, EventArgs e)
    {

        dtFirst = (DataTable)ViewState["dtFirst"];
        dtPlatit = (DataTable)ViewState["dtPlatit"];

        int i = 0;
        foreach (GridViewRow row in GridViewTerm.Rows)
        {
            int myId;
            int FacturaId = Int32.Parse(row.Cells[0].Text); //exception 
            if (((CheckBox)row.FindControl("chkRowPlatita")).Checked)
            {
                dtPlatit.Rows.Add(GridViewTerm.DataKeys[row.DataItemIndex].Value, ((Label)row.FindControl("lblNume")).Text, ((Label)row.FindControl("lblDataSc")).Text, ((Label)row.FindControl("lblSumaP")).Text);
                dtFirst.Rows.RemoveAt(row.DataItemIndex - i);
                i++;

                updaterow(FacturaId, "true");
            }
        }
        GridViewPlatit.DataSource = dtPlatit;
        GridViewPlatit.DataBind();
        GridViewTerm.DataSource = dtFirst;
        GridViewTerm.DataBind();
        ViewState["dtFirst"] = dtFirst;
        ViewState["dtPlatit"] = dtPlatit;
    }

    private void updaterow(int FacturaId, String Platit)
    {
        String CS = ConfigurationManager.ConnectionStrings["BudgetTrackDBConnectionString1"].ConnectionString;
        String updatedata = "Update Facturi set Platit='" + Platit + "' where FacturaId=" + FacturaId;
        SqlConnection con = new SqlConnection(CS);
        con.Open();
        SqlCommand cmd = new SqlCommand();
        cmd.CommandText = updatedata;
        cmd.Connection = con;
        cmd.ExecuteNonQuery();

    }

How to solve my issue?

        <asp:GridView ID="GridViewTerm" runat="server" HorizontalAlign="Center" DataKeyNames="FacturaId" OnSorting="GridViewTerm_Sorting" AutoGenerateColumns="False" AllowSorting="True" AllowPaging="True" BackColor="White" BorderColor="#3366CC" BorderStyle="None" BorderWidth="1px" CellPadding="4" EmptyDataText="Nu există facturi!" OnPageIndexChanging="OnPageIndexChanging" PageSize="4">
            <Columns>
                <asp:TemplateField HeaderText="Factura ID" Visible="false">
                    <ItemTemplate>
                        <asp:Label ID="lblId" runat="server" Text='<%# Eval("FacturaId") %>' ></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Nume">
                    <ItemTemplate>
                        <asp:Label ID="lblNume" runat="server" Text='<%# Eval("Nume") %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField> 
                <asp:TemplateField HeaderText="Data Scadenta">
                    <ItemTemplate>
                        <asp:Label ID="lblDataSc" runat="server" Text='<%# Eval("Data_Scadenta") %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Suma">
                    <ItemTemplate>
                        <asp:Label ID="lblSumaP" runat="server" Text='<%# Eval("Suma_Plata") %>'></asp:Label>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Plătită">
                    <ItemTemplate>
                        <asp:CheckBox ID="chkRowPlatita" runat="server" AutoPostBack="true" OnCheckedChanged="chkRowPlatita_CheckedChanged" />
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:TemplateField HeaderText="Parțial plătită">
                    <ItemTemplate>
                        <asp:CheckBox ID="chkRowPartialPlatita" runat="server" AutoPostBack="true" OnCheckedChanged="chkRowPartialPlatita_CheckedChanged" />
                    </ItemTemplate>
                </asp:TemplateField> 
            </Columns> 
        </asp:GridView>