MPC1000 JJOS1: MP says "File not found" but shows, and works

I've got an MPC1000 with JJOS 1 v 4.99 installed. I'm putting WAV files from my computer onto the memory card via card reader and the files show up and play fine. When I put the card into the MPC, it shows the files as being present, but outputs the message, "File not found!!!"

On the other hand, a few songs that I put on the card DO work.

Any ideas?

16 bit 44.1Khz?
name more than 16 characters?

Ah! The title was more than 16 characters! Thanks!