Tried to do this with Global.asax.cs and Umbraco.Web.UmbracoApplication, but the result is the same. It seems the error is triggered when the handler is called.

Code:

public class UmbracoApplication : Umbraco.Web.UmbracoApplication
{
    protected override void OnApplicationStarted(object sender, EventArgs e)
    {
        LogHelper.Info("Started");
        base.OnApplicationStarted(sender, e);

        // Same result without the EventHandler wrapper:
        this.BeginRequest += new EventHandler(UmbracoApplication_BeginRequest);
        LogHelper.Info("Event handler added");
    }

    private void UmbracoApplication_BeginRequest(object sender, EventArgs e)
    {
    }
}

Log:

2013-05-16 14:06:24,526 [10] INFO  Umbraco.Site.UmbracoApplication - [Thread 76] Started
2013-05-16 14:06:24,526 [10] INFO  Umbraco.Site.UmbracoApplication - [Thread 76] Event handler added

Error:

[NullReferenceException: Object reference not set to an instance of an object.]
   System.Web.PipelineStepManager.ResumeSteps(Exception error) +1239
   System.Web.HttpApplication.BeginProcessRequestNotification(HttpContext context, AsyncCallback cb) +95
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +186

Found something that worked when extending Umbraco.Web.UmbracoApplication (but unfortunately not IApplicationEventHandler): Ignore the EventHandler properties and implement handler methods prefixed with "Application_", like so:

public void Application_BeginRequest(object sender, EventArgs e)
{
// ...
}

Now if only I could figure out how to do that when implementing IApplicationEventHandler :-/

Could it be related to http://stackoverflow.com/questions/7005646/nullreferenceexception-pipelinestepmanager-resumesteps-at-godaddy ?

Anyone?

public class Foobar : IApplicationEventHandler {
    public void OnApplicationInitialized(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext) {
        LogHelper.Info<Foobar>("Initialized");
    }

    public void OnApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext) {
        LogHelper.Info<Foobar>("Starting");
    }

    public void OnApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext) {
        LogHelper.Info<Foobar>("Started");

        // In ASP.NET there can by multiple instances of the HttpApplication.
        // The ApplicationInit event will be raised on every HttpApplication.Init()
        UmbracoApplicationBase.ApplicationInit += Init;
    }

    private void Init(object sender, EventArgs eventArgs) {
        var app = (HttpApplication) sender;
        app.BeginRequest += (s, e) => { };
    }
}

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