Im trying to create my own custom error 404 handler. I've followed the "how to"-guide here on Our Umbraco but I can't get it to work.

This is the code I have right now.

My handlerclass:

namespace AVWebUmbraco.UmbracoExtensions.Eventhandlers
{
public class NotFound : INotFoundHandler
{
    private int redirectId;

    public bool Execute(string url)
    {
        var server = HttpContext.Current.Request.ServerVariables["SERVER_NAME"].ToLower();
        if (server == "www.mydomain1.com")
        {
            redirectId = 1234; // the id of the 404 and search page from domain1.com
            return true;
        }
        if (server == "www.mydomain2.com")
        {
            redirectId = 5678; // the id of the 404 and search page from domain2.com
            return true;
        }
        return false;
    }

    public bool CacheUrl
    {
        get { return false; }
    }

    public int redirectID
    {
        get { return redirectID; }
    }
  }
}

404handlers.config:

<NotFoundHandlers>
<notFound assembly="umbraco" type="SearchForAlias" />
<notFound assembly="umbraco" type="SearchForTemplate"/>
<notFound assembly="umbraco" type="SearchForProfile"/>
<notFound assembly="umbraco" type="handle404"/>
<notFound assembly="AVWebUmbraco" namespace="AVWebUmbraco.UmbracoExtensions.Eventhandlers" type="NotFound" />
</NotFoundHandlers>

The error I get is: