I can create a new sketch in my documents/libraries/ folder. But if I then make a change and try to save that sketch, I get the error message:
Some files are marked "read-only" so you'll need to re-save this sketch to another location.
From googling this error, the most common problem seems to be when people are trying to save to the examples directory. But I'm trying to save to my libraries folder.
What else can cause this error?