I've added my own custom section to Umbraco and have added the Delete functionality to the tree. This all works fine, but once I have deleted the item from the tree, I want the iframe on the right to reload so that the deleted item is no longer shown. I thought that I could use returnUrl for this but for some reason it's not working. Any help would be really appreciated!

Here's a copy of my code:

    public class FormBuilderTasks : umbraco.interfaces.ITaskReturnUrl
    {
        private string _alias;
        private int _parentID;
        private int _typeID;
        private int _userID;
       
        public int UserId
        {
            set { _userID = value; }
        }

        public int TypeID
        {
            set { _typeID = value; }
            get { return _typeID; }
        }

        public int ParentID
        {
            set { _parentID = value; }
            get { return _parentID; }
        }

        public string Alias
        {
            get { return _alias; }
            set { _alias = value; }
        }

        #region ITaskReturnUrl Members

        private string _returnUrl = "";

        public string ReturnUrl
        {
            get { return _returnUrl; }
        }

        #endregion

       
        /// <summary>
        /// Create a new form
        /// </summary>
        public bool Save()
        {
            return true;
        }

        /// <summary>
        /// Delete a form
        /// </summary>
        public bool Delete()
        {
            string filePath = HttpContext.Current.Server.MapPath("/umbraco/formBuilder/forms/" + ParentID + ".xml");

            try
            {
                File.Delete(filePath);
                _returnUrl = "/umbraco/formBuilder/AdminContainer.aspx";
                return true;
            }
            catch
            {
                return false;
            }
    }