SaveAs under Windows errs with 'The file may be read-only'

1. I have a new (untitled) document

2. My scripts tries to perform 'SaveAs(filepath)'

3. A error popup appears "The file may be raed-only, or another user may have it open. Please save the document with a different name or in a different folder."

When I use the EXACT SAME filepath, and go manually to the menu - SaveAs, and paste the file path there, it works perfectly.

I'm 100% sure that the given filepath does not exist before the script runs.

We can't back-check right now, but the same script worked fine in Illustrator CC 2018, is that possible?

Again, it just happens on Windows!

Best regards,

Stefan