Facebook fan page tab - not getting the params

Question

My fan page tab is an Asp.Net page and am not receiving any of the tabbed profile params such as fb_sig_user, fb_sig_profile_user from Facebook.. http://wiki.developers.facebook.com/index.php/Tabbed_Profile

before I did one php tab and my tab received all the params..

My page has the following code and I added it to a fan page as a tab..

    System.Text.StringBuilder sb = new System.Text.StringBuilder();
    foreach (string key in Request.Params.AllKeys)
    {
        sb.Append(key).Append(": ").Append(Request.Params[key]).Append("<br />");
    }
    Response.Write(sb.ToString());

Now when I open the tab I am seeing only the usual SERVER VARIABLES and not any facebook posted params..

am I doing anything wrong here?