Getting hidden field value on next page

Question

Hi

I have a hidden value field on a page. On submit I post to a different page. On the page I've posted to I do a Request.Form but I do not get the value just a null value.

This is the initial page

<div id="booking_content_wrapper">
        <form id="mainForm" name="mainForm" runat="server" action="Cancellation.aspx">
            <h2>Paid Bookings</h2>
            <table cellpadding="0" cellspacing="0" border="0" id="booking_table">
                <tr>
                    <th width="110">Enquiry No.</th>
                    <th width="250">Establishment</th>
                    <th width="110">Arrival Date</th>
                    <th width="20">Confirmed</th>
                    <th>Action</th>
                </tr>
       
                 <asp:Literal ID="PaidBookingsResults" runat="server"></asp:Literal>
            </table>       
            <asp:HiddenField runat="server" ID="ResID" EnableViewState="true" />
        </form>
    </div>
<script>
    function ViewCancellation(sResID) {
        document.getElementById("<%=ResID.ClientID%>").value = sResID;
        document.getElementById("mainForm").submit();
    }

</script>   

The javascript ViewCancellation function is set to a hyperlink in the code behind. The function will have a value like this,<a href=\"#\" onclick=\"ViewCancellation(54666);return false;\">cancel</a>

On the page I'm posting to I'm doing this

string sResID = "";

    protected void Page_Load(object sender, EventArgs e)
    {
        HttpContext context = HttpContext.Current;
        sResID = context.Request.Form["ResID"] != null ? context.Request.Form["ResID"] : "";
        sResID = Regex.Replace(sResID, "/[^A-Z]\\d-/g", "");

        context.Response.Write(sResID);

    }

sResID gets no value because context.Request.Form["ResID"] is null. How can I get the value to this page. I've enabledviewstate