Starsector 0.97a is out! (02/02/24); New blog post: Simulator Enhancements (03/13/24)
Are you using any mods/have you tweaked your files?
I'd suggest trying to run without the mods to narrow down where the problem is. If it still happens w/o them, you could reinstall to a different location just to grab a valid copy of weapon_data.csv (assuming you don't want to do a clean reinstall and lose your changes...)