Mega/Adafruit FONA808 Undeleteable/Unreadable SMS

I have a Mega and an Adafruit #2524 FONA808 board. I am using the FONATest sketch supplied as a FONA example. The sketch reports that there is a SMS but I cannot read or delete it.
I am using the latest FONA library 1.3.10.

Can anyone help shed some light on this?