I ran into an issue that may be helpful to others.
I've been using an approved 16g card without incident. As that card was nearly full, I decided to delete the files while the card was still in my computer (Mac). Move to Trash, card empty, eject disk, put card back in deck, done.
Well, I get about :40 minutes into recording at my next event and it stopped recording. My card was 'full'.
When I got home, I backed up that :40 minute file, reinserted the card back into the deck and formatted the card again. Boom! Card has 16+ hours of record time available.
Lesson: Always check the Remaining Time, located in the upper right of the display.
And.... I believe I may begin the habit of deleting files from the card while it is in the deck.