Joe, is it your web server or ColdFusion returning the 404? What happens if you put just a .htm file in the specified location and browse to that?
TBH, I'm kinda with Carl on this... CF mappings should have no bearing on whether a file is browsable or not. CF mappings are related to how ColdFusion finds its resources from a code perspective (eg: <cfinclude> or createObject(), etc), and not to do with what's browsable and what's not. That's the web server's job.
From memory - and I don't have CF10 here to test - CF10 is less able to process files outside its context root than JRun is, so I could see a potential problem with this on CF10 (and I'm gonna have to remain vague on this, as I cannot quickly test it), but CF9 should not behave any differently than CF8 in this regard. And I hasten to add on neither CF8 nor CF9 do CF mappings have anything to do with the browsability of files. Sorry. That's just how it is.
Over and above all that: does the problematic box connect to the system as the same account as the boxes that work? IE: is it just a network permissions issue?
--
Adam
