facebook fbjs script dosent work with runat="server" attribute

Question

hi, I am trying making facebook application with asp.net. My script code dosent run with form runat="server" attribute. I check with firebug and I am getting this error :

XXX_form is null.

my code :

<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">

<script>

        function displayError(title, message, context) 
        { 
            new Dialog(Dialog.DIALOG_CONTEXTUAL).setContext(context).showMessage(title, message );
        }

        function check_form(form) 
        {     


            if ( form == null) { form = document.getElementById('formDataContent');}

            var params=form.serialize();
            if (params.textSelectedFriend==null || params.textSelectedFriend=='' )
            {
                displayError("Error", "Please select a Comrade!" , document.getElementById('data_selected_content1') );
                return false;
            }
            else 
            {
                return true;
            }
        }

</script>
<form runat="server" id="formDataContent">

<fb:friend-selector idname="textSelectedFriend" />

<asp:Button ID="buttonSend" runat="server" Text="Send" CssClass="inputsubmit" OnClick="buttonSend_Click" />

    </form>

</asp:Content>

thanks in advance

onder