Why would an aspx file return 404 (“The page cannot be found”)

Question

Why when I access an aspx (e.g., http://www.example.com/foo.aspx - not the real site) through IE6 would I get a 404 Error (i.e., \"The page cannot be found\") in IIS6

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Answer 1

I had bin\roslyn compiler missing. Adding that all worked fine.