Getting the very same error, tried a ton of earlier versions as well as the betas, tried uploading working config files... Nada, this is the only post treating of 1.6.9, and I've seen something about 1.6.7 needing gson.jar ( http://dev.bukkit.org/server-mods/factions/tickets/130-factions-will-not-enable/ ) -> tried it, downloaded it, uploaded it, not working
Please note each time I wipe the server clean, and try again with a new version (always installing Vault with Factions for full support)