Just as a follow-up...
My knowledge of ASP.NET is limited, so this question may sound silly - is the code that launches Excel running on the server, or is it 'script' (lack of a better term) running on the browser?
If it's the former, 'maybe' that would explain why you see it in the task manager, but you don't see it launching?
I would have thought a rights issue would keep it from loading in the first place, but it's just a question.
Kevin