Hi Dirk,

When changing how I register the PageNotFound code it shows me the custom 404 page when no template is set, wich is great. But, if I browse to a node that doesn't exists I will get a iis error instead of the custom 404 page with a 500 response?

In the web.config I have set the httpsErrors to:

<httpErrors errorMode="DetailedLocalOnly" existingResponse="PassThrough">

Could this be the source of the problem now?

Have you checked the part about web.routing inside umbracoSettings.config? there should be comments on how to configure it inside the config file

Yes, they look like this:

<web.routing 
    trySkipIisCustomErrors="true" 
    internalRedirectPreservesTemplate="false" 
    disableAlternativeTemplates="false" 
    disableFindContentByIdPath="false" 
    umbracoApplicationUrl="" 
    disableRedirectUrlTracking="true">
</web.routing>

Ugh, actually the code below won't run if i navigate to a url that has no content, only if the node has no template. I'm trying to run the code when either the node is missing or the node has no template.

using System.Linq;
using Umbraco.Core;
using Umbraco.Web.Routing;

namespace PyramidWebsiteClassTests
{
    /// <summary>
    /// Umbraco content finder implementation for 404 pages in multi-lingual sites
    /// Assumes each site has a document type with alias of "PageNotFound" in the root of the site (under home node)
    /// </summary>
    public class PageNotFound : IContentFinder
    {
        /// <summary>
        /// Used to find the correct 404 page when a page cannot be found in Umbraco
        /// </summary>
        /// <param name="contentRequest">The current Umbraco context</param>
        /// <returns>The 404 page</returns>
        public bool TryFindContent(PublishedContentRequest contentRequest)
        {

            //Check request cannot be found
            if (contentRequest.PublishedContent == null)
            {
                var domain = contentRequest.UmbracoDomain.RootContentId;

                if (domain != null)
                {
                    var home = contentRequest.RoutingContext.UmbracoContext.ContentCache.GetById(domain.Value);

                    if (home != null)
                    {
                        //Get the 404 node
                        var notFoundNode = home.Children.FirstOrDefault(x => x.DocumentTypeAlias == "pageNotFound_d");

                        if (notFoundNode != null)
                        {
                            //Set Response Status to be HTTP 404
                            //contentRequest.SetResponseStatus(404, "Not Found");

                            //Set the node to be the not found node
                            contentRequest.PublishedContent = notFoundNode;
                        }
                    }
                }
            }

            return contentRequest.PublishedContent != null;
        }

        /// <summary>
        /// Also need to register the handler in OnApplicationStarting
        /// </summary>
        public class StartUpApplication : ApplicationEventHandler
        {
            protected override void ApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
            {
                //ContentFinderResolver.Current.InsertTypeBefore<ContentFinderByNotFoundHandlers, PageNotFound>();
                ContentLastChanceFinderResolver.Current.SetFinder(new PageNotFound());
            }
        }
    }
}

Ah, good you got it working!