Hi Sof,
This error can occur for two reasons:
- 1. The wrong board is selected in the Tools > Boards menu. It should be Teensy 3.6
- 2. The SDFat library for Arduino is missing, or you have the wrong version installed. The developers of SDFat recently released version 2 and located it in the master branch of their old repository (confusing!) You need SDFat version 1 (see the warning in the readme with directions to download v1).
I'll update the wiki to reflect this.
Note: If you purchased the analog output module pre-assembled from us, WavePlayer firmware is pre-installed.
-Josh