When you hit "Clear User Data" check the box in the window that says display all drives.. Hit Refresh.. Make sure you choose the right drive when they show up in the window.. Select "OK" to proceed. Once the card goes through this initial process, You'll just Write to scanner as normal from then on..
I would also caution that you verify that Sentinel is set to the correct target model before using the 'Clear User Data' and writing your Favorite(s) list to the card.