I had the same problem. I found that when I enabled ASP and ASP.NET the new handler mappings were not propogating down to the web site after they were enabled. I deleted the site and re-created it. The newly created site inherited the new mappings and I can get the pages now. I have no idea why the mappings...

Well, the problem with the cache disappeared after rebooting my machine. But the 404.3 persists... ASP.NET is installed. I verified this several times. Nevertheless I only get this annoying 404.3. I need further help with this issue. Thanks a lot!