Can you go to Settings/Permalinks and click Save Changes. That will flush the permalinks.
You could look at the ‘Debug wp_redirect‘ plugin.
Edit: Another idea is to determine what template file is in use. I have a small function plugin that adds debug comments to the header and footer for logged in Editors or Admins.
I have uploaded it to pastebin.com. Copy it to a text file and upload it to wp-content/mu-plugins or to wp-content/plugins and then activate it. Reload your page and search for “get_template_name” and tell us the filenames listed on that line and the 2 lines after it.