Q:

Why are these check-boxes not being checked from code-behind? 

I have a website written in ASP.NET MVC and I have a parameter set to the page in question that specifies what the preceding page is.  The reasoning for this is so when a user clicks an image from a particular page, the loaded page will automatically check the appropriate check box using javascript (jQuery particularly). 
Here is the code that gets and sets the parameter:
<script type="text/C#" runat="server">
    protected string Referrer = string. Empty;
    protected override void OnLoad(EventArgs e)
    {
        try
        {
            Referrer = Request. UrlReferrer. Segments[2].ToLower();
        }
        catch (System. Exception)
        {

            Referrer = string. Empty;
        }
        base. OnLoad(e);
    }
</script>

Next, here is the collection of check-boxes:
<div id="interestSelect1" class="interestPad">
        <%= Html. CheckBoxFor(model => model. Interests[0])%>
        <label for="Interests_0_">Insulation</label>
        <%= Html. CheckBoxFor(model => model. Interests[1])%>
        <label for="Interests_1_">Windows</label>
        <%= Html. CheckBoxFor(model => model. Interests[2])%>
        <label for="Interests_2_">Siding</label>
        <%= Html. CheckBoxFor(model => model. Interests[3])%>
        <label for="Interests_3_">Roofing</label>
    </div>
    <div class="clear">
    </div>
    <div id="interestSelect2" class="interestPad">
        <%= Html. CheckBoxFor(model => model. Interests[4])%>
        <label for="Interests_4_">Gutters/Protection</label>
        <%= Html. CheckBoxFor(model => model. Interests[5])%>
        <label for="Interests_5_">Patio Doors</label>
    </div>

When rendered in the browser, here is what each of the check-boxes look like:
<input id="Interests_0_" name="Interests[0]" type="checkbox" value="true" />
<input name="Interests[0]" type="hidden" value="false" />
<label for="Interests_0_">Insulation</label>

Here is the javascript that I am using, that is not working:
<script type="text/javascript">
    var ref = '<%= Referrer %>';
    $(document).ready(function () {
        switch (ref) {
            case "insulation":
                $('Interests_0_').attr('checked', 'checked');
                break;
            case "windows":
                $('Interests_1_').attr('checked', 'checked');
                break;
            case "siding":
                $('Interests_2_').attr('checked', 'checked');
                break;
            case "roofing":
                $('Interests_3_').attr('checked', 'checked');
                break;
            case "gutters":
                $('Interests_4_').attr('checked', 'checked');
                break;
            case "patiodoors":
                $('Interests_5_').attr('checked', 'checked');
                break;
            default:
                // do nothing, not valid ref
        }
    });
</script>

I am obviously doing something completely wrong, can anyone point me in the right direction? 
Thanks! 
EDIT: Looks like another JS file that was on a MasterPage that was called before my JS block was causing the boxes to not be checked.  The main problem was forgetting the # identifier. 

A:

#id selectors need a # prefix, like this:
$('#Interests_0_').attr('checked', 'checked');

Without the #, it's an element selector, looking for a <Interests_0_> element. 
You can slim it down overall with an object though, like this:
var ref = '<%= Referrer %>';
var map = {"insultation":"#Interests_0_",
           "windows":"#Interests_1_",
           "siding":"#Interests_2_",
           "roofing":"#Interests_3_",
           "gutters":"#Interests_4_",
           "patiodoors":"#Interests_5_"};
$(function () {
   var id = map[ref];
   if(id) $(id).attr('checked', true);
});

