I wanted to share some of my recent experience with everyone since this cost me great deal of time and stumped many. I recently tried to add some aspx pages to my existing Cognos environment in IIS. This was not smooth.
The challenge here is that if you are going to do this you need to have the extensions correct in IIS. But you cannot just add the ASP.net extension in the we service extension area of IIS. You must also register this if it is not already showing up in IIS. Normally when you install this will show up here but not all the time.