Hi,

I found the same issue on this post( http://our.umbraco.org/forum/using/ui-questions/19391-Usercontrol-not-working-in-umbraco?p=0#comment102880 )

I will come with details. I create a macro which contains a form 2 hidden fields and a button.

It renders content on frontend when controller is without form tag. When I insert it it shows me on content tab: No macro content available for wysiwyg editing.

Here is CODE

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="SignUpButton.ascx.cs" Inherits="HoteloProModules.SignUpButton.SignUpButton" %>

<div class="div_center">
    <form name="formSignUpp" id="formSignUp" runat="server" action="" method="post">
        <div class="btn_class_a">
            <div class="btn_left"></div>
            <asp:HiddenField ID="hidMaxNrOfRooms" Value=""  runat="server"/>
            <asp:HiddenField ID="hidAccountType" Value="" runat="server"/>
            <asp:Button CssClass="btn_center" Text="SIGN TEMP" runat="server" ID="btnSignUp"/>
            <div class="btn_right"></div>
        </div>
    </form>
</div>

and code behind CODE

    public partial class SignUpButton : System.Web.UI.UserControl
    {
        private Int16 MaxNrOfRooms, AccountType;

        /// <summary>
        /// 5, 25, 50
        /// </summary>
        public Int16 _MaxNrOfRooms
        {
            get { return MaxNrOfRooms; }
            set { MaxNrOfRooms = value; }
        }
        /// <summary>
        /// 1 2 or 3
        /// </summary>
        public Int16 _AccountType
        {
            get { return AccountType; }
            set { AccountType = value; }
        }
        protected void Page_Load(object sender, EventArgs e)
        {
            btnSignUp.Text= umbraco.library.GetDictionaryItem("SignUp").ToUpper();
            hidMaxNrOfRooms.Value = _MaxNrOfRooms.ToString();
            hidAccountType.Value = _AccountType.ToString();
            //
            formSignUp.Action = "https://" + HoteloProGenerals.WebAppRootNoScheme + "Register.aspx";
        }
    }

The reason why I need there a form is because I want a button that when is pressed to send/redirect/post to an address transfering values.