Thank you for buying the game. Unfortunately I have no real idea why it won't work on your The64 but will look into is as soon as possible. Sorry for the inconvenience.
Glad to hear that you can play it at least. I have googled a bit and this may be connected to the true drive emulation in The64 (Vice). This thread describes how it was solved for someone (though for other games), but it seems to be a bit fiddly and I have no possibility to verify it unfortunately.
https://www.lemon64.com/forum/viewtopic.php?p=1024158&sid=d4a0af18517fc87193037a...