I created a simple web forms application and created a class library project inside this solution as a project reference. This class library project is my HttpModule. The idea of this is so I can step into my HttpModule code. Here's what my solution looks like:

In Default.aspx.cs, I threw an exception to see if OnError in my HttpModule would catch it (which it doesn't catch it - it never hits my breakpoint inside OnError):

Finally, here's my web.config:

QUESTION: Can anyone tell me what I might be doing wrong? I'm not entirely confident with my web.config entry. Does the web.config entry look okay? Could adding this HttpModule via a project reference be causing an issue?
Are you running your application in Integrated mode? If so, you have to add your http module to the system.webServer/modules configuration section, rather than system.web/httpModules