I've got this nice 404 handler that works fine on my local machine. When I deploy to my live server, it does not work. I looked everywhere, those 2 websites (live and local) are almost identical (other than connection string and stuff). (To be super sure, I too a .bak of my live DB and successfully ran with that locally.)

The code runs on 2 files.

Umbraco404HandlerHook.cs

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

namespace MyNamespace.Code
{
    public class Umbraco404HandlerHook : ApplicationEventHandler
    {
        protected override void ApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            ContentLastChanceFinderResolver.Current.SetFinder(new Umbraco404Handler());
            base.ApplicationStarting(umbracoApplication, applicationContext);
        }
    }
}

And Umbraco404Handler.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Web;
using Umbraco.Core;
using Umbraco.Web;
using Umbraco.Web.Routing;

// Needs interfaces and cms references

namespace MyNamespace.Code
{
    public class Umbraco404Handler : IContentFinder
    {

        public bool TryFindContent(PublishedContentRequest contentRequest)
        {

            Utilities.LogText("Umbraco404Handler - 1");

            // Safety check, this should never occur
            if (contentRequest != null)
            {

                Utilities.LogText("Umbraco404Handler - 2");

                // Check request is a 404
                if (contentRequest.Is404)
                {

                    Utilities.LogText("Umbraco404Handler - 3");

                    // Need a domain to get the 404 page
                    if (contentRequest.Domain != null)
                    {

                        Utilities.LogText("Umbraco404Handler - 4");

                        var domainNode = contentRequest.RoutingContext.UmbracoContext.ContentCache.GetById(contentRequest.Domain.RootNodeId);
                        if (domainNode != null)
                        {

                            Utilities.LogText("Umbraco404Handler - 5");

                            // Todo: Have this field label come from a config?
                            int notFoundNodeId = domainNode.AsDynamic().page404; // Unset content picker, cast to int, will be 0
                            if (notFoundNodeId != 0)
                            {

                                Utilities.LogText("Umbraco404Handler - 6");

                                // Get the 404 node
                                var notFoundNode = contentRequest.RoutingContext.UmbracoContext.ContentCache.GetById(notFoundNodeId);
                                if (notFoundNode != null)
                                {

                                    Utilities.LogText("Umbraco404Handler - 7 - " + notFoundNode.Name);

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

                                }
                            }
                            else
                            {
                                // Todo: No specified 404, this could have a fallback in settings?                    
                            }
                        }

                    }
                    else 
                    { 
                        // Todo: No domain, this could have a fallback in settings?                    
                    }

                }

            }

            // Finally, we return weather we have found a node to use for this request
            return contentRequest.PublishedContent != null;
        }

    }
}

I added these logging calls to figure out what was going on on my live site and whenever a 404 is hit, the code traces up to #7 with no problem, but I keep seeing the default IIS 404 page:

404 - File or directory not found.

What could be causing this issue, I mean... the code runs, and correctly, but the live site 404 seems to be bypassed by something else...

Any help will be much appreciated!