This could be the same thing I found. If you're running your
site on IIS and you have made a virtual directory to point to your
components, apparently there is a CF8 bug that makes AJAX calls
unable to find them given these configuration circumstances. I
heard (sorry - I can't remember where I read all this!) that an
official Adobe CF Updater is in beta right now that will resolve
this. Until then... switch to Apache? I'm considering doing this on
my development server, as we've made this move on the production
servers already.
If you're not using IIS with virtual directories pointing to
your CFCs then I'm afraid I don't have any suggestions.