I had an interesting emailed question today. Here's a paraphrased one sentence version of the question: Why does an ASP.NET Runtime issue surface in IIS 8.0 Integrated Pool for an application we have run successfully on previous versions of IIS and classic mode in IIS 8.0 ? It's less interesting that they've moved from IIS6 to IIS8 and more significant that they've moved from Classic Mode to the Integrated Mode pipeline. So, the short answer. These pipelines are different and if you write an app expecting the behavior of one pipeline and the move it, your observed behavior will likely be different when you move it to the new pipeline.