More and more I like into this and I can only come to the conclusion that IIS and the .NET framework cannot handle simultaneous hits when a new DLL is in effect. Basically, when we look at this pattern, we can easily see that a deadlock is in effect and that IIS and the .NET framework cannot handle it.

Id:7caf1385-a192-4803-b90d-296e20d5ddad Application Start at 7/13/2010 12:11:06 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:11:06 PM
Id:00000000-0000-0000-0000-000000000000 Application PreRequestHandlerExecute at 7/13/2010 12:11:10 PM
Id:7caf1385-a192-4803-b90d-296e20d5ddad Application End at 7/13/2010 12:11:17 PM
Id:ba97c70a-c508-4134-b27a-48eef5d0cc27 Application Start at 7/13/2010 12:11:21 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:11:21 PM
Id:00000000-0000-0000-0000-000000000000 Application PreRequestHandlerExecute at 7/13/2010 12:11:25 PM
Id:ba97c70a-c508-4134-b27a-48eef5d0cc27 Application End at 7/13/2010 12:11:26 PM
Id:868586b7-5360-43c2-bda3-b46c424f5af6 Application Start at 7/13/2010 12:11:30 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:11:30 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:11:30 PM
Id:00000000-0000-0000-0000-000000000000 Application PreRequestHandlerExecute at 7/13/2010 12:11:32 PM
Id:00000000-0000-0000-0000-000000000000 Application PreRequestHandlerExecute at 7/13/2010 12:11:38 PM
Id:868586b7-5360-43c2-bda3-b46c424f5af6 Application End at 7/13/2010 12:11:39 PM
Id:af00e0af-cd1f-4b68-b88e-cdb422fec052 Application Start at 7/13/2010 12:11:39 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:11:39 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:11:39 PM
Id:00000000-0000-0000-0000-000000000000 Application PreRequestHandlerExecute at 7/13/2010 12:11:42 PM
Id:00000000-0000-0000-0000-000000000000 Application PreRequestHandlerExecute at 7/13/2010 12:11:48 PM
Id:af00e0af-cd1f-4b68-b88e-cdb422fec052 Application End at 7/13/2010 12:13:59 PM
Id:cc5030c2-f1bf-45b5-b9ac-0a26a47599d9 Application Start at 7/13/2010 12:14:06 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:14:06 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:14:06 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:14:06 PM
Id:00000000-0000-0000-0000-000000000000 Application BeginRequest at 7/13/2010 12:14:06 PM
Id:00000000-0000-0000-0000-000000000000 Application PreRequestHandlerExecute at 7/13/2010 12:14:10 PM
Id:00000000-0000-0000-0000-000000000000 Application PreRequestHandlerExecute at 7/13/2010 12:14:10 PM

We see that the application End() event was fired when a new DLL was in effect. Then, the Start() event was fired. Then, we can see the four clicks I did on four .aspx pages. However, only two succeeded to go as far as PreRequestHandlerExecute(). So, this is a sign of a deadlock. My feeling is that many are simply not doing live updates and they are probably shutting down IIS before doing the update. In my case, an update takes 4 seconds to get in effect. So, I wouldn't want to shut down IIS for that. Also, we want to make it invisible to the user, but an extra 4 seconds, when a new DLL is sent.