"Illustrator could partially read this file."

Whenever I save my document, I can't then reopen it - it just says that Illustrator could only partially read the file.

Nothing happens when I'm saving, no crashes or anything and I can continue working on my stuff when it's saved.

The file icons are also greyed out as if there isn't a program to open it, if that makes sense?

I should also note that I am using artboards, so I don't know if it's something to do with that?

I'm super new to Illustrator so please bear with me!