I have an EU Zumo 550, with the latest CN Europe maps installed (v2010.1). I've now bought the latest CN NA maps (v2010.1 on DVD) to put onto the SD card. I installed the maps onto my MacBook Pro, attached the Zumo and also put the 4Gb SD card into the slot on the side of the MBP. When I opened Road Trip, it told me that the maps were locked and did I want to unlock them. Well, yeah So I clicked on the button to unlock them online. From the Garmin web page, I found my Zumo device, which put the Unit ID into the appropriate field. I then entered the serial number fro the white sticker on the back of the DVD cover (the number starting S/N) and the 8-character product key listed on the green sticker. When I clicked the <Unlock Map> button, the page refreshed with an error: Invalid combination of Unit Id and Serial Number . Any ideas?