I was getting the "access denied" error every time I attempted to edit a page on a particular Contribute website. Then, after reading the thread at Just Skins, I deleted/published old drafts associated with that website. Now everything works correctly.
The draft that caused the problem had 1) the lock removed by a Dreamweaver user, 2) template changes since the draft was created, and 3) nothing in common with the pages where I received the error.
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North America
Europe, Middle East and Africa
Asia Pacific