In the configuration, check Languages and Locale -> Language and see what you have for Language Files and Languages. Neither of these should be set (they should say Restore). These are for multi-lingual sites and if enabled, then glFusion looks for topics ending with the 2 character language code, for example _en.
If those look OK, I would double check those permissions again. Make sure the topic allows anonymous access and that each story allows it as well.
Finally, clear the Template Cache, I doubt this would have anything to do with it, but just to be sure.
If none of this works, any chance I could poke around the site?