Invalid data on index - incorrect header signature

I am at a complete loss. Unable to save any project in phpmaker. I am suddenly getting the message: Invalid data on index - incorrect header signature. While it started with a project i am working on now, I have opened already completed projects, clicked saved and got the same message.

I am using phpmaker 2019.0.10. However, i tried phpmaker 2020 on the same projects and getting the same error.

https://discourse.hkvstore.com/t/invalid-data-in-index-on-save/576/1