Why can event handlers only be bound to HttpApplication events during IHttpModule initialization?

Question

This is just another "working in dev server, why not working in IIS" type question.

I created a nice DAL using NHibernate as described here. When creating an ISession, I hook up an event handler to the HttpApplication.EndRequest to take care of cleaning it up.

However, I deployed my site to IIS and it says:

Event handlers can only be bound to HttpApplication events during IHttpModule initialization.

I completely understand what the message is saying, but I can't undestrand why.

I can subscribe to a Button's event in any time, why can't I subscribe to an event of the HttpApplication?

I would be very grateful if someone could shed some light on this.

And I also wonder, why is it working with the development server and not with IIS 7?

EDIT: Now that two months has passed, I still haven't received any useful answers. :(
Is this issue really that hard?

Answer 1

You're trying to use the HttpApplication outside its initialization pipeline. Just don't do it. As the error says, bind your events during IHttpModule initialization.