Getting MIDI Data from Casio CT-S1 Keyboard

My iOS app using CoreMIDI is able to receive MIDI messages from various keyboards, but I have just received a note from a customer notifying me that my app does not appear to receive MIDI messages from his Casio CT-S1 keyboard. I am stymied on how to diagnose and fix this issue. Clearly there must be something amiss in my CoreMIDI integration. I thought perhaps someone else might have encountered a similar odd situation such as this.

If it helps, here is my CoreMIDI integration code. Thanks!

Regards,

Brad