I encountered a few issues when starting to develop on Windows Vista. I had my whole enviornment setup and I decided to write a quick little asp.net app and test it out….Once I hit F5 in studio – I got a msgbox:

Unable to cast object of type ‘System.Web.HttpDebugHandler’ to type ‘System.Web.HttpApplication’.

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Unable to start debugging on the web server.  

[InvalidCastException]: Unable to cast object of type ‘System.Web.HttpDebugHandler’ to type ‘System.Web.HttpApplication’.   at System.Web.Hosting.PipelineRuntime.ExecuteStateHandler(IntPtr& managedRequestContext, IntPtr nativeRequestContext, IntPtr moduleData, Int32 flags)

So I figured it was probably something to do with the new Integrated mode in IIS and VS2005 has no clue about it. So I moved the app to a new Application Pool in IIS7 that runs in ISAPI mode and now everything works!