Thanks for the reply, Mark. That's what the problem was; I had configured iFly to save the data on my external SD card and that's been working without incident since I started using iFly several months ago. When I checked the storage location setting after this most recent "all data out of date" download, it had saved the data to the internal memory. I moved it all back to the SD card (using the menu option w/in iFly, not manually) and all seems to be well again.
The question remains, though... WHY did it happen? A bit concerning if it didn't happen at home, but rather in the air. Not that I'm relying on it, but still....