You're getting this with a Drupal web site installation?
I ran into an "Access Denied. You are not authorized to access this page" problem once, too. An authenticated user with permissions to edit all content node types was not seeing the "Edit" link on the content pages, even after properly logging in. Although I checked the access control settings a half dozen times, I finally noticed there was no check in the "Filters" box and wondered, so I put one there. Everything worked again and the link showed up. But that gave him access to the administer filters menu, too. So I went to Site Configuration - Input Formats and configured each of the different input formats to be available to authenticated users. Apparently, if content was generated by an admin using one of the non-default filters, users won't get access to edit the pages.
Send me an email at userfriendly@gazettenet.com.
In addition to getting an emailed answer to your question, it may appear in my column, "User Friendly" in the Daily Hampshire Gazette's weekly magazine, Hampshire Life.
Of course, I'll post answers here, as well so that the search engines will find them--and folks won't have to wander all over the Internet looking for answers to the problems that plague us. Thanks for your help with this.