Yup... Operator Error! Here's what happened.
For several songs, I used registrations that were not part of the factory set that comes with the keyboard. The files are on a USB drive plugged into the keyboard. As many of you do, I am sure, I searched through files listening to see what would work well for my arrangement and when I found it, I saved it to the Registration. In many cases, I also saved it to the USER area of the keyboard storage. However, there are some that I simply forgot to save so the keyboard couldn't find them. There were also a few that were saved to the USER area, but had not been mapped there. I have gone back and copied all of the Style files from the USB drive to the keyboard user area making sure that each is correctly mapped to the registration. Lesson learned!
Thanks very much for the quick replies.