Stack with the same name loop

[Sean Cole (Pi)]

Hi all,
Can someone give the definitive answer as to what to choose when I save my
stack with a save as to create a new iterative version and it comes up with
the prompt :
      A stack with the same name as the one you are trying to load is
already open.
            Save    Purge    Cancel

Whatever I do it ends up in a loop of asking this. I'm bored of having to
force close LC to get over this. What is supposed to happen if I press
Save? What is supposed to happen if I press Purge? And what about Cancel?
I've never understood the need for purge AND save. Purge from what? Save
and close? purge and close? It's just not clear to me as a long time user
let alone a new user.

Btw, just to avoid unnecessary responses, I already know I can just make a
copy in the finder, clear LC memory and load that one in. My question is
just trying to get an understanding of this prompt.

Thanks

Sean