Are you confusing updating the Sync ii software with the navigation maps. I recently updated my Sync software from the Ford website. You have to download it onto a USB thumb drive and update it that way. I think the error message you are getting is for the Sync software. Call a Ford dealer and ask if they charge for the update. I didn't see much difference in the software, it now has the ability to reboot the system, so you may not even need the update.
The navigation is a separate update. Back in December I ordered the 4 CD discs from Ford for 150 and updated the navigation maps.