I just tried it (for the first time) with Excel 2000 using an Excel file with chart and calculation pages. It looks like it created a "master" file with the same filename.htm plus a sub-folder of .htm files that the master file called to display the piece being viewed. i.e., there were separate .htm files for each sheet.
I would assume that you need most (maybe all of these) for the web version to work correctly. Try renaming the dependent sheets one at a time and see what happens.