What do I do when I try to open a magic file I previously made and it comes up empty? This is accompanied by an error message saying

...has a zero timestamp; it should be written out to establish a correct timestamp.

Is there a solution to this?

I'm guessing that if it came up empty that it really is empty (which you can confirm by looking at the contents of the file). The question is: Was it non-empty before, and how was it created originally? Feel free to post the file (or what's left of it, anyway).