Invalid project file "filename.cpr"!

I get this error when trying to open a project on Cubase LE AI 9. It’s a project I’ve been working on for over a year, that is way ahead of my other projects (since it’s been my main focus for a while).

I have not added any new sounds since I began to edit (so it shouldn’t be a size issue), these files I have now are the same ones that I had already over a year ago. Nothing new added lately or anything like that.

Why do I get this error that stops me from getting into my project? This shit truly scares me tbh. My latest backup is from over 6 months ago (the song was really rough and bad back then), so it would kill me if all the work I’ve made since was for nothing. You can’t even compare that version with this one I had/have now.

My backup and all my other projects that have been sidelined are working just fine to open. So it’s only this single one (that was basically finished, just the last few touches left) I can’t get into at all. I’ve sent a mail to Steinberg support but they seem to be really slooow, so would appreciate if someone else knew what could be done here!