I just installed this great package on a 4.5 site, without realising it didn't support version 4.5. I just tweaked the code slightly to support 4.5, and thought I'd share it.

Here the code for the main redirect class

 private bool m_cacheUrl;
        private int m_redirectId;
 

        public bool CacheUrl
        {
            get
            {
                return this.m_cacheUrl;
            }
        }


        public int redirectID
        {
            get
            {
                return this.m_redirectId;
            }
        }

        public Redirect301Handler()
        {
            this.m_cacheUrl = true;
            this.m_redirectId = -1;
        }


        public bool Execute(string url)
        {
            string str = url;
            if (str.Length > 0)
            {
                if (str.Substring(0, 1) == "/")
                {
                    str = str.Substring(1, str.Length - 1);
                }
                HttpContext.Current.Trace.Write("umbraco301MovedPermanently", "'" + str + "'");
                string domainName = HttpContext.Current.Request.ServerVariables["SERVER_NAME"];
                string str3 = string.Empty;
                if (Domain.Exists(domainName))
                {
                    str3 = "//*[@id='" + Domain.GetRootFromDomain(domainName) + "']";
                    this.m_cacheUrl = false;
                }
                string xpath = string.Format("{0}//*[contains(concat(',', umbraco301MovedPermanently, ','), ',{1},')]", str3, str.Replace(".aspx", string.Empty).ToLower());
                XmlNode node = umbraco.content.Instance.XmlContent.DocumentElement.SelectSingleNode(xpath);
                if ((node != null) && int.TryParse(node.Attributes.GetNamedItem("id").Value, out this.m_redirectId))
                {
                    string str5 = umbraco.library.NiceUrl(this.m_redirectId);
                    this.m_cacheUrl = true;
                    HttpContext.Current.Response.Clear();
                    HttpContext.Current.Response.StatusCode = 0x12d;
                    HttpContext.Current.Response.Status = "301 Moved Permanently";
                    HttpContext.Current.Response.AddHeader("Location", str5);
                    HttpContext.Current.Response.End();
                    return true;
                }
            }
            return false;
        }