cant bind to datagrid?

<mesh:SecurePanel runat="server" ID="retentionInvoiceDue" WebMasters="true" Admins="true" style="text-align:left; font-size:small;"><a class="alert" ID="a1">Alerts</a><br><asp:Panel ID="panelToPromptRetentionInvoiceDue" runat="server"
                CssClass="retentionLinksOnHomePage" Visible="true"><asp:DataGrid ID="datagridToPromptRetentionInvoiceDue" runat="server"
                    AutoGenerateColumns="false" GridLines="None" ShowHeader="false"><Columns><asp:TemplateColumn><ItemTemplate><span>Site<asp:LinkButton ID="promptRententionInvoiceLink" CommandArgument='<%# Bind ("id") %>' OnCommand="getSessionVariableForWorkSiteID" runat="server"><asp:Label id="labelBindfromHomeToInvoice" runat="server" Text="<%# Bind('Site_Name') %>"/></asp:LinkButton>retention due for invoicing</span></ItemTemplate></asp:TemplateColumn></Columns></asp:DataGrid></asp:Panel></mesh:SecurePanel>

In cs file I have in page load:

Context db = new Context();

        var allWorkSites =
            (from worksites in db.Work_Sites
             select worksites).Distinct().ToList();

        List<Object> chosenInvoicesForRetention = new List<Object>();

        foreach (Work_Site worksite in allWorkSites)
        {
            if (!worksite.Invoicing_Complete)
            {
                Invoice lastInvoice = worksite.Invoices.OrderBy(w => w.id).LastOrDefault();

                if (lastInvoice != null)
                {
                    if (lastInvoice.Invoice_Date < DateTime.Now.AddMonths(0 - worksite.Number_of_Months))
                    {
                        chosenInvoicesForRetention.Add(worksite);
                    }
                }

            }
        }

        if (chosenInvoicesForRetention.Count == 0)
        {
            panelToPromptRetentionInvoiceDue.Visible = false;
        }

        else
        {
            datagridToPromptRetentionInvoiceDue.DataSource = chosenInvoicesForRetention;
            datagridToPromptRetentionInvoiceDue.DataBind();
        }

    }

Why am I getting the error: panelToPromptRetentionInvoiceDue & datagridToPromptRetentionInvoiceDue does not exist??

I should mention that this code works fine from a different page on my prject, i just copied it over as I want to use it again, but change the table it is being linked too...why would it work from one page and not another?