Error "Bad name index -1/66" when packaging

Can anyone please help with this error that appeared out of nowhere. The project was packaging without a problem then this started happening. I’ve seen some “answers” for similar questions but they do not apply to me as I cannot tell which files were last changed and I cannot afford to migrate all project files as this is a big project. What does the -1/66 mean and can it help identify the file(s) causing the issue?