I've had the same problem with Best Western Lake Buena Vista. Sometimes the reservation number works and sometimes it doesn't. My recommendation is to first call the B resort and ask if they have a different confirmation number that you can try. If that doesn't work then you need to call Disney at 407-939-4357. When it asks what you need help with say "Link a reservation". Good Luck! It is annoying that a year after announcing the Disney Springs hotels are part of the 60 day FP and "extra magic" that we still have this issue.