The message if they are booked should be the same as when other restaurants are full - something like no tables available. If it’s saying error then that sounds like a problem with the search tool. I was in the same situation as you- had a H&V without F! because the F! Packages weren’t out at my 180+. The day they became available nothing was showing up so I had to cancel my H&V and immediately rebook it as H&V + F! I’m not sure if this will always happen if the F! Packages are limited but it did work for me. I did it the day the F! Packages were released though. I totally understand the anxiety about canceling though. You may want to call dining and have them do it, although I ended up having to call back several times because they didn’t realize when I canceled it would then immediately pop up as part of the package. Perhaps if it doesn’t then they can just rebook it without F! for you so it doesn’t get snatched up. Hope that makes sense. It was a crazy morning!