ROM in an unreadable format
What it means
The ROM is there, but in an archive the emulator cannot open.
Why it happens
The emulator only reads .zip archives. A ROM in .7z or .rar is ignored, as if it did not exist.
How Pincab Toolbox detects it
No .zip archive named after the ROM, but a .7z or .rar file with the same name in the ROMs folder.
Automatic repair
Repair, included in the Pincab Toolbox licence, can fix this one for you. Your files are backed up first, and the fix can be undone.
Check your own pincab
Pincab Toolbox is a free Windows scanner for Visual Pinball X and PinUP Popper. It finds and explains problems like this one. No account, no telemetry.
Download for freeCovered: Visual Pinball X (10.x) and PinUP Popper. Not covered: Future Pinball, Pinball FX, Visual Pinball 9 and the other frontends (PinballX, PinballY).