Latest build soon to complete tonight should fix some issues to improve emulating your program in DOSBox-X.

There exists a version of CWSDPMI patched for PC-98 systems, can you try this in DOSBox-X and see if it works? It works for me, at least.

gist.github.com/lpproj/d4220...

What DOS extender is the real PC-9821 system using?

CWSDPMI is writing to ports 20h and 21h to set up the interrupt controller as if talking to IBM PC hardware, which doesn't work on PC-98 where those I/O ports are at 00h and 02h instead.

Notice that when your program actually does run, you can crash it right away with that error by pressing a key on the keyboard.

Can you try your program with a PC-98 aware version of CWSDPMI instead?

It's using CWSDPMI.EXE.

CWSDPMI isn't redirecting the IRQ interrupt vectors, which means while running there is a conflict between IRQ 0-7 and the protected mode exceptions.

"Coprocessor Overrun" means the extender saw INT 9h happen.

INT 9h is also the keyboard interrupt.

DOSBox-X should probably not include those on the Z: drive in PC-98 mode for that reason, and should include instead PC-98 versions of those where available.

Part of the problem is that those DOS extenders are IBM PC versions. They happen to work on PC-98 except that the code to print exception information on screen doesn't work and often hangs on PC-98.

DOSBox-X by default provides CWSDPMI, DOS4GW, and DOS32A. Which one is it running? Try running DOSBox-X with the --debug command line option and open the console, then run the game. It should say what files were opened and which one of the DOS extenders was involved.

What DOS extender are you using?

Is it a version designed for PC-98 systems?

DOSBox-X developer here. DOSBox-X has a PC-98 emulation mode, does it work there?

Better yet, find a Linux box and plug it in there. There's no autorun in Linux.

Of course worst case scenario, it could be one of those USB killer sticks...

Would it have anything to do with social media in the last 8 years? Or perhaps streaming services?