Duplicate App to an already existing ID on Google app engine
You say you already used that id before.
If you havent deleted that app just use that one to load your new code there. You will need to delete existing datastore data etc.
I made a blog  in Python and I am running it off of Google App Engine. When I started, I put a random ID, just because I was experimenting. Lately, my blog got a bit popular and I wanted to change the ID. I wanted to duplicate my app, but the problem is that I already registered that ID a while ago with google. How can I duplicate it even though the name already exists. 
Thanks,
Liam