MIDI file export

Hi all, I am trying to create a medley of drum tracks for a performance using a keyboard. I have made the medley by importing midi files and routing the output through a midi bus of 16 tracks. The midi output of this plays fine through my keyboard, however this is off a desktop, and live, I would just like a midi file playing through the keyboard off a USB stick. I recorded the bus to a separate midi track and exported it, and it played fine in anvil studio. However, when I plugged the USB stick into the keyboard I got an error saying the data had not been loaded properly.

Is there a better way to export a midi file that might work?

This is a valid and the correct way with Ardour 5 to merge/combine MIDI.

That would indicate that the .mid file is fine.

What keyboard is that?
Do other .mid files work on the same USB key? If so is there an obvious difference between those files?
Perhaps try to re-export the .mid from anvil studio.

What keyboard are you using is definitely the most important question. My guess is the USB needs to be formatted a certain way to work with that keyboard.

I have tried midi format 0 exports from anvil to no avail, and also passed the files through a Yamaha format checker that checks the compatibility of files for my keyboard. No errors show. I have several other functioning midi files on this USB stick so it is confusing me why it won’t work.
For the record , it’s a psr s900.
I will try a different USB today.
UPDATE: I have switched to using the midi medley function in gnmidi. It’s not perfect but it works.