Editing Omnioutliner file - Can't save changes (option to duplicate to save)

Using OO 5.15. I was editing an outline that I created. All fine. Until I made some edits and said I did not have permission to save it. Option to duplicate and save was given (and worked). Why could I suddenly not save my own file?

Hard to say without knowing more about your setup but generally, it would be because the file was locked in some way or the folder it was in was locked. Probably the former in this case as it let you create a duplicate (presumably in the same place).

If you’re seeing this issue continue, I’d suggest contacting omni (Help > Contact Omni) and seeing if they can help.