The MIDI file should start with the MThd signature.
You can mostly solve this by removing the unrecognized header bytes (I've used HexFiend for this) :
https://hexfiend.com/
Re: Please support Genos/PSR SX900 Chord Looper Bank (.clb) files
Thanks for looking into this Bruno.
However given I just shared the .clb files that I obtained directly from the PSR SX as transferred to my Mac via official Yamaha software- would it be possible for you to instead modify MIDIKit so that it just takes care of this nonstandard header behaviour directly? either accepting it "as is" or doing this modification to the file yourself?
But given any feature you add in the future in order to be able to edit .clb files directly would need to save the file in exactly the same internal format as the Yamaha arranger's ( and certain Clavinovas ) create and save them - its probably best to leave the header structure exactly as yamaha designed it.
I'll be raising an extra feature request - to ask you to also consider adding a graphic way to edit any of the up-to-eight chord progressions contained in a .clb file in the manner of arranger apps like BandInABox or iRealPro.
I think you would find there is a new market of customers for you if you do this in Yamaha land!
And you could also consider just releasing this new functionality as a new app - and I suggest could charge a fair bit for it. As no-one including Yamaha is doing anything like this at the moment.